OpenCloudOS-Kernel/include/linux/rcutiny.h

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rcu: "Tiny RCU", The Bloatwatch Edition This patch is a version of RCU designed for !SMP provided for a small-footprint RCU implementation. In particular, the implementation of synchronize_rcu() is extremely lightweight and high performance. It passes rcutorture testing in each of the four relevant configurations (combinations of NO_HZ and PREEMPT) on x86. This saves about 1K bytes compared to old Classic RCU (which is no longer in mainline), and more than three kilobytes compared to Hierarchical RCU (updated to 2.6.30): CONFIG_TREE_RCU: text data bss dec filename 183 4 0 187 kernel/rcupdate.o 2783 520 36 3339 kernel/rcutree.o 3526 Total (vs 4565 for v7) CONFIG_TREE_PREEMPT_RCU: text data bss dec filename 263 4 0 267 kernel/rcupdate.o 4594 776 52 5422 kernel/rcutree.o 5689 Total (6155 for v7) CONFIG_TINY_RCU: text data bss dec filename 96 4 0 100 kernel/rcupdate.o 734 24 0 758 kernel/rcutiny.o 858 Total (vs 848 for v7) The above is for x86. Your mileage may vary on other platforms. Further compression is possible, but is being procrastinated. Changes from v7 (http://lkml.org/lkml/2009/10/9/388) o Apply Lai Jiangshan's review comments (aside from might_sleep() in synchronize_sched(), which is covered by SMP builds). o Fix up expedited primitives. Changes from v6 (http://lkml.org/lkml/2009/9/23/293). o Forward ported to put it into the 2.6.33 stream. o Added lockdep support. o Make lightweight rcu_barrier. Changes from v5 (http://lkml.org/lkml/2009/6/23/12). o Ported to latest pre-2.6.32 merge window kernel. - Renamed rcu_qsctr_inc() to rcu_sched_qs(). - Renamed rcu_bh_qsctr_inc() to rcu_bh_qs(). - Provided trivial rcu_cpu_notify(). - Provided trivial exit_rcu(). - Provided trivial rcu_needs_cpu(). - Fixed up the rcu_*_enter/exit() functions in linux/hardirq.h. o Removed the dependence on EMBEDDED, with a view to making TINY_RCU default for !SMP at some time in the future. o Added (trivial) support for expedited grace periods. Changes from v4 (http://lkml.org/lkml/2009/5/2/91) include: o Squeeze the size down a bit further by removing the ->completed field from struct rcu_ctrlblk. o This permits synchronize_rcu() to become the empty function. Previous concerns about rcutorture were unfounded, as rcutorture correctly handles a constant value from rcu_batches_completed() and rcu_batches_completed_bh(). Changes from v3 (http://lkml.org/lkml/2009/3/29/221) include: o Changed rcu_batches_completed(), rcu_batches_completed_bh() rcu_enter_nohz(), rcu_exit_nohz(), rcu_nmi_enter(), and rcu_nmi_exit(), to be static inlines, as suggested by David Howells. Doing this saves about 100 bytes from rcutiny.o. (The numbers between v3 and this v4 of the patch are not directly comparable, since they are against different versions of Linux.) Changes from v2 (http://lkml.org/lkml/2009/2/3/333) include: o Fix whitespace issues. o Change short-circuit "||" operator to instead be "+" in order to fix performance bug noted by "kraai" on LWN. (http://lwn.net/Articles/324348/) Changes from v1 (http://lkml.org/lkml/2009/1/13/440) include: o This version depends on EMBEDDED as well as !SMP, as suggested by Ingo. o Updated rcu_needs_cpu() to unconditionally return zero, permitting the CPU to enter dynticks-idle mode at any time. This works because callbacks can be invoked upon entry to dynticks-idle mode. o Paul is now OK with this being included, based on a poll at the Kernel Miniconf at linux.conf.au, where about ten people said that they cared about saving 900 bytes on single-CPU systems. o Applies to both mainline and tip/core/rcu. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: Josh Triplett <josh@joshtriplett.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: avi@redhat.com Cc: mtosatti@redhat.com LKML-Reference: <12565226351355-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-10-26 10:03:50 +08:00
/*
* Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, you can access it online at
* http://www.gnu.org/licenses/gpl-2.0.html.
rcu: "Tiny RCU", The Bloatwatch Edition This patch is a version of RCU designed for !SMP provided for a small-footprint RCU implementation. In particular, the implementation of synchronize_rcu() is extremely lightweight and high performance. It passes rcutorture testing in each of the four relevant configurations (combinations of NO_HZ and PREEMPT) on x86. This saves about 1K bytes compared to old Classic RCU (which is no longer in mainline), and more than three kilobytes compared to Hierarchical RCU (updated to 2.6.30): CONFIG_TREE_RCU: text data bss dec filename 183 4 0 187 kernel/rcupdate.o 2783 520 36 3339 kernel/rcutree.o 3526 Total (vs 4565 for v7) CONFIG_TREE_PREEMPT_RCU: text data bss dec filename 263 4 0 267 kernel/rcupdate.o 4594 776 52 5422 kernel/rcutree.o 5689 Total (6155 for v7) CONFIG_TINY_RCU: text data bss dec filename 96 4 0 100 kernel/rcupdate.o 734 24 0 758 kernel/rcutiny.o 858 Total (vs 848 for v7) The above is for x86. Your mileage may vary on other platforms. Further compression is possible, but is being procrastinated. Changes from v7 (http://lkml.org/lkml/2009/10/9/388) o Apply Lai Jiangshan's review comments (aside from might_sleep() in synchronize_sched(), which is covered by SMP builds). o Fix up expedited primitives. Changes from v6 (http://lkml.org/lkml/2009/9/23/293). o Forward ported to put it into the 2.6.33 stream. o Added lockdep support. o Make lightweight rcu_barrier. Changes from v5 (http://lkml.org/lkml/2009/6/23/12). o Ported to latest pre-2.6.32 merge window kernel. - Renamed rcu_qsctr_inc() to rcu_sched_qs(). - Renamed rcu_bh_qsctr_inc() to rcu_bh_qs(). - Provided trivial rcu_cpu_notify(). - Provided trivial exit_rcu(). - Provided trivial rcu_needs_cpu(). - Fixed up the rcu_*_enter/exit() functions in linux/hardirq.h. o Removed the dependence on EMBEDDED, with a view to making TINY_RCU default for !SMP at some time in the future. o Added (trivial) support for expedited grace periods. Changes from v4 (http://lkml.org/lkml/2009/5/2/91) include: o Squeeze the size down a bit further by removing the ->completed field from struct rcu_ctrlblk. o This permits synchronize_rcu() to become the empty function. Previous concerns about rcutorture were unfounded, as rcutorture correctly handles a constant value from rcu_batches_completed() and rcu_batches_completed_bh(). Changes from v3 (http://lkml.org/lkml/2009/3/29/221) include: o Changed rcu_batches_completed(), rcu_batches_completed_bh() rcu_enter_nohz(), rcu_exit_nohz(), rcu_nmi_enter(), and rcu_nmi_exit(), to be static inlines, as suggested by David Howells. Doing this saves about 100 bytes from rcutiny.o. (The numbers between v3 and this v4 of the patch are not directly comparable, since they are against different versions of Linux.) Changes from v2 (http://lkml.org/lkml/2009/2/3/333) include: o Fix whitespace issues. o Change short-circuit "||" operator to instead be "+" in order to fix performance bug noted by "kraai" on LWN. (http://lwn.net/Articles/324348/) Changes from v1 (http://lkml.org/lkml/2009/1/13/440) include: o This version depends on EMBEDDED as well as !SMP, as suggested by Ingo. o Updated rcu_needs_cpu() to unconditionally return zero, permitting the CPU to enter dynticks-idle mode at any time. This works because callbacks can be invoked upon entry to dynticks-idle mode. o Paul is now OK with this being included, based on a poll at the Kernel Miniconf at linux.conf.au, where about ten people said that they cared about saving 900 bytes on single-CPU systems. o Applies to both mainline and tip/core/rcu. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: Josh Triplett <josh@joshtriplett.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: avi@redhat.com Cc: mtosatti@redhat.com LKML-Reference: <12565226351355-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-10-26 10:03:50 +08:00
*
* Copyright IBM Corporation, 2008
*
* Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
*
* For detailed explanation of Read-Copy Update mechanism see -
* Documentation/RCU
rcu: "Tiny RCU", The Bloatwatch Edition This patch is a version of RCU designed for !SMP provided for a small-footprint RCU implementation. In particular, the implementation of synchronize_rcu() is extremely lightweight and high performance. It passes rcutorture testing in each of the four relevant configurations (combinations of NO_HZ and PREEMPT) on x86. This saves about 1K bytes compared to old Classic RCU (which is no longer in mainline), and more than three kilobytes compared to Hierarchical RCU (updated to 2.6.30): CONFIG_TREE_RCU: text data bss dec filename 183 4 0 187 kernel/rcupdate.o 2783 520 36 3339 kernel/rcutree.o 3526 Total (vs 4565 for v7) CONFIG_TREE_PREEMPT_RCU: text data bss dec filename 263 4 0 267 kernel/rcupdate.o 4594 776 52 5422 kernel/rcutree.o 5689 Total (6155 for v7) CONFIG_TINY_RCU: text data bss dec filename 96 4 0 100 kernel/rcupdate.o 734 24 0 758 kernel/rcutiny.o 858 Total (vs 848 for v7) The above is for x86. Your mileage may vary on other platforms. Further compression is possible, but is being procrastinated. Changes from v7 (http://lkml.org/lkml/2009/10/9/388) o Apply Lai Jiangshan's review comments (aside from might_sleep() in synchronize_sched(), which is covered by SMP builds). o Fix up expedited primitives. Changes from v6 (http://lkml.org/lkml/2009/9/23/293). o Forward ported to put it into the 2.6.33 stream. o Added lockdep support. o Make lightweight rcu_barrier. Changes from v5 (http://lkml.org/lkml/2009/6/23/12). o Ported to latest pre-2.6.32 merge window kernel. - Renamed rcu_qsctr_inc() to rcu_sched_qs(). - Renamed rcu_bh_qsctr_inc() to rcu_bh_qs(). - Provided trivial rcu_cpu_notify(). - Provided trivial exit_rcu(). - Provided trivial rcu_needs_cpu(). - Fixed up the rcu_*_enter/exit() functions in linux/hardirq.h. o Removed the dependence on EMBEDDED, with a view to making TINY_RCU default for !SMP at some time in the future. o Added (trivial) support for expedited grace periods. Changes from v4 (http://lkml.org/lkml/2009/5/2/91) include: o Squeeze the size down a bit further by removing the ->completed field from struct rcu_ctrlblk. o This permits synchronize_rcu() to become the empty function. Previous concerns about rcutorture were unfounded, as rcutorture correctly handles a constant value from rcu_batches_completed() and rcu_batches_completed_bh(). Changes from v3 (http://lkml.org/lkml/2009/3/29/221) include: o Changed rcu_batches_completed(), rcu_batches_completed_bh() rcu_enter_nohz(), rcu_exit_nohz(), rcu_nmi_enter(), and rcu_nmi_exit(), to be static inlines, as suggested by David Howells. Doing this saves about 100 bytes from rcutiny.o. (The numbers between v3 and this v4 of the patch are not directly comparable, since they are against different versions of Linux.) Changes from v2 (http://lkml.org/lkml/2009/2/3/333) include: o Fix whitespace issues. o Change short-circuit "||" operator to instead be "+" in order to fix performance bug noted by "kraai" on LWN. (http://lwn.net/Articles/324348/) Changes from v1 (http://lkml.org/lkml/2009/1/13/440) include: o This version depends on EMBEDDED as well as !SMP, as suggested by Ingo. o Updated rcu_needs_cpu() to unconditionally return zero, permitting the CPU to enter dynticks-idle mode at any time. This works because callbacks can be invoked upon entry to dynticks-idle mode. o Paul is now OK with this being included, based on a poll at the Kernel Miniconf at linux.conf.au, where about ten people said that they cared about saving 900 bytes on single-CPU systems. o Applies to both mainline and tip/core/rcu. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: Josh Triplett <josh@joshtriplett.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: avi@redhat.com Cc: mtosatti@redhat.com LKML-Reference: <12565226351355-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-10-26 10:03:50 +08:00
*/
#ifndef __LINUX_TINY_H
#define __LINUX_TINY_H
#include <linux/cache.h>
static inline unsigned long get_state_synchronize_rcu(void)
{
return 0;
}
static inline void cond_synchronize_rcu(unsigned long oldstate)
{
might_sleep();
}
static inline unsigned long get_state_synchronize_sched(void)
{
return 0;
}
static inline void cond_synchronize_sched(unsigned long oldstate)
{
might_sleep();
}
static inline void rcu_barrier_bh(void)
{
wait_rcu_gp(call_rcu_bh);
}
static inline void rcu_barrier_sched(void)
{
wait_rcu_gp(call_rcu_sched);
}
rcu: Add a TINY_PREEMPT_RCU Implement a small-memory-footprint uniprocessor-only implementation of preemptible RCU. This implementation uses but a single blocked-tasks list rather than the combinatorial number used per leaf rcu_node by TREE_PREEMPT_RCU, which reduces memory consumption and greatly simplifies processing. This version also takes advantage of uniprocessor execution to accelerate grace periods in the case where there are no readers. The general design is otherwise broadly similar to that of TREE_PREEMPT_RCU. This implementation is a step towards having RCU implementation driven off of the SMP and PREEMPT kernel configuration variables, which can happen once this implementation has accumulated sufficient experience. Removed ACCESS_ONCE() from __rcu_read_unlock() and added barrier() as suggested by Steve Rostedt in order to avoid the compiler-reordering issue noted by Mathieu Desnoyers (http://lkml.org/lkml/2010/8/16/183). As can be seen below, CONFIG_TINY_PREEMPT_RCU represents almost 5Kbyte savings compared to CONFIG_TREE_PREEMPT_RCU. Of course, for non-real-time workloads, CONFIG_TINY_RCU is even better. CONFIG_TREE_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 6170 825 28 7023 kernel/rcutree.o ---- 7026 Total CONFIG_TINY_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 2081 81 8 2170 kernel/rcutiny.o ---- 2183 Total CONFIG_TINY_RCU (non-preemptible) text data bss dec filename 13 0 0 13 kernel/rcupdate.o 719 25 0 744 kernel/rcutiny.o --- 757 Total Requested-by: Loïc Minier <loic.minier@canonical.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-06-30 07:49:16 +08:00
static inline void synchronize_rcu_expedited(void)
{
rcu: Add a TINY_PREEMPT_RCU Implement a small-memory-footprint uniprocessor-only implementation of preemptible RCU. This implementation uses but a single blocked-tasks list rather than the combinatorial number used per leaf rcu_node by TREE_PREEMPT_RCU, which reduces memory consumption and greatly simplifies processing. This version also takes advantage of uniprocessor execution to accelerate grace periods in the case where there are no readers. The general design is otherwise broadly similar to that of TREE_PREEMPT_RCU. This implementation is a step towards having RCU implementation driven off of the SMP and PREEMPT kernel configuration variables, which can happen once this implementation has accumulated sufficient experience. Removed ACCESS_ONCE() from __rcu_read_unlock() and added barrier() as suggested by Steve Rostedt in order to avoid the compiler-reordering issue noted by Mathieu Desnoyers (http://lkml.org/lkml/2010/8/16/183). As can be seen below, CONFIG_TINY_PREEMPT_RCU represents almost 5Kbyte savings compared to CONFIG_TREE_PREEMPT_RCU. Of course, for non-real-time workloads, CONFIG_TINY_RCU is even better. CONFIG_TREE_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 6170 825 28 7023 kernel/rcutree.o ---- 7026 Total CONFIG_TINY_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 2081 81 8 2170 kernel/rcutiny.o ---- 2183 Total CONFIG_TINY_RCU (non-preemptible) text data bss dec filename 13 0 0 13 kernel/rcupdate.o 719 25 0 744 kernel/rcutiny.o --- 757 Total Requested-by: Loïc Minier <loic.minier@canonical.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-06-30 07:49:16 +08:00
synchronize_sched(); /* Only one CPU, so pretty fast anyway!!! */
}
rcu: Add a TINY_PREEMPT_RCU Implement a small-memory-footprint uniprocessor-only implementation of preemptible RCU. This implementation uses but a single blocked-tasks list rather than the combinatorial number used per leaf rcu_node by TREE_PREEMPT_RCU, which reduces memory consumption and greatly simplifies processing. This version also takes advantage of uniprocessor execution to accelerate grace periods in the case where there are no readers. The general design is otherwise broadly similar to that of TREE_PREEMPT_RCU. This implementation is a step towards having RCU implementation driven off of the SMP and PREEMPT kernel configuration variables, which can happen once this implementation has accumulated sufficient experience. Removed ACCESS_ONCE() from __rcu_read_unlock() and added barrier() as suggested by Steve Rostedt in order to avoid the compiler-reordering issue noted by Mathieu Desnoyers (http://lkml.org/lkml/2010/8/16/183). As can be seen below, CONFIG_TINY_PREEMPT_RCU represents almost 5Kbyte savings compared to CONFIG_TREE_PREEMPT_RCU. Of course, for non-real-time workloads, CONFIG_TINY_RCU is even better. CONFIG_TREE_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 6170 825 28 7023 kernel/rcutree.o ---- 7026 Total CONFIG_TINY_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 2081 81 8 2170 kernel/rcutiny.o ---- 2183 Total CONFIG_TINY_RCU (non-preemptible) text data bss dec filename 13 0 0 13 kernel/rcupdate.o 719 25 0 744 kernel/rcutiny.o --- 757 Total Requested-by: Loïc Minier <loic.minier@canonical.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-06-30 07:49:16 +08:00
static inline void rcu_barrier(void)
{
rcu: Add a TINY_PREEMPT_RCU Implement a small-memory-footprint uniprocessor-only implementation of preemptible RCU. This implementation uses but a single blocked-tasks list rather than the combinatorial number used per leaf rcu_node by TREE_PREEMPT_RCU, which reduces memory consumption and greatly simplifies processing. This version also takes advantage of uniprocessor execution to accelerate grace periods in the case where there are no readers. The general design is otherwise broadly similar to that of TREE_PREEMPT_RCU. This implementation is a step towards having RCU implementation driven off of the SMP and PREEMPT kernel configuration variables, which can happen once this implementation has accumulated sufficient experience. Removed ACCESS_ONCE() from __rcu_read_unlock() and added barrier() as suggested by Steve Rostedt in order to avoid the compiler-reordering issue noted by Mathieu Desnoyers (http://lkml.org/lkml/2010/8/16/183). As can be seen below, CONFIG_TINY_PREEMPT_RCU represents almost 5Kbyte savings compared to CONFIG_TREE_PREEMPT_RCU. Of course, for non-real-time workloads, CONFIG_TINY_RCU is even better. CONFIG_TREE_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 6170 825 28 7023 kernel/rcutree.o ---- 7026 Total CONFIG_TINY_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 2081 81 8 2170 kernel/rcutiny.o ---- 2183 Total CONFIG_TINY_RCU (non-preemptible) text data bss dec filename 13 0 0 13 kernel/rcupdate.o 719 25 0 744 kernel/rcutiny.o --- 757 Total Requested-by: Loïc Minier <loic.minier@canonical.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-06-30 07:49:16 +08:00
rcu_barrier_sched(); /* Only one CPU, so only one list of callbacks! */
}
rcu: Add a TINY_PREEMPT_RCU Implement a small-memory-footprint uniprocessor-only implementation of preemptible RCU. This implementation uses but a single blocked-tasks list rather than the combinatorial number used per leaf rcu_node by TREE_PREEMPT_RCU, which reduces memory consumption and greatly simplifies processing. This version also takes advantage of uniprocessor execution to accelerate grace periods in the case where there are no readers. The general design is otherwise broadly similar to that of TREE_PREEMPT_RCU. This implementation is a step towards having RCU implementation driven off of the SMP and PREEMPT kernel configuration variables, which can happen once this implementation has accumulated sufficient experience. Removed ACCESS_ONCE() from __rcu_read_unlock() and added barrier() as suggested by Steve Rostedt in order to avoid the compiler-reordering issue noted by Mathieu Desnoyers (http://lkml.org/lkml/2010/8/16/183). As can be seen below, CONFIG_TINY_PREEMPT_RCU represents almost 5Kbyte savings compared to CONFIG_TREE_PREEMPT_RCU. Of course, for non-real-time workloads, CONFIG_TINY_RCU is even better. CONFIG_TREE_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 6170 825 28 7023 kernel/rcutree.o ---- 7026 Total CONFIG_TINY_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 2081 81 8 2170 kernel/rcutiny.o ---- 2183 Total CONFIG_TINY_RCU (non-preemptible) text data bss dec filename 13 0 0 13 kernel/rcupdate.o 719 25 0 744 kernel/rcutiny.o --- 757 Total Requested-by: Loïc Minier <loic.minier@canonical.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-06-30 07:49:16 +08:00
static inline void synchronize_rcu_bh(void)
rcu: "Tiny RCU", The Bloatwatch Edition This patch is a version of RCU designed for !SMP provided for a small-footprint RCU implementation. In particular, the implementation of synchronize_rcu() is extremely lightweight and high performance. It passes rcutorture testing in each of the four relevant configurations (combinations of NO_HZ and PREEMPT) on x86. This saves about 1K bytes compared to old Classic RCU (which is no longer in mainline), and more than three kilobytes compared to Hierarchical RCU (updated to 2.6.30): CONFIG_TREE_RCU: text data bss dec filename 183 4 0 187 kernel/rcupdate.o 2783 520 36 3339 kernel/rcutree.o 3526 Total (vs 4565 for v7) CONFIG_TREE_PREEMPT_RCU: text data bss dec filename 263 4 0 267 kernel/rcupdate.o 4594 776 52 5422 kernel/rcutree.o 5689 Total (6155 for v7) CONFIG_TINY_RCU: text data bss dec filename 96 4 0 100 kernel/rcupdate.o 734 24 0 758 kernel/rcutiny.o 858 Total (vs 848 for v7) The above is for x86. Your mileage may vary on other platforms. Further compression is possible, but is being procrastinated. Changes from v7 (http://lkml.org/lkml/2009/10/9/388) o Apply Lai Jiangshan's review comments (aside from might_sleep() in synchronize_sched(), which is covered by SMP builds). o Fix up expedited primitives. Changes from v6 (http://lkml.org/lkml/2009/9/23/293). o Forward ported to put it into the 2.6.33 stream. o Added lockdep support. o Make lightweight rcu_barrier. Changes from v5 (http://lkml.org/lkml/2009/6/23/12). o Ported to latest pre-2.6.32 merge window kernel. - Renamed rcu_qsctr_inc() to rcu_sched_qs(). - Renamed rcu_bh_qsctr_inc() to rcu_bh_qs(). - Provided trivial rcu_cpu_notify(). - Provided trivial exit_rcu(). - Provided trivial rcu_needs_cpu(). - Fixed up the rcu_*_enter/exit() functions in linux/hardirq.h. o Removed the dependence on EMBEDDED, with a view to making TINY_RCU default for !SMP at some time in the future. o Added (trivial) support for expedited grace periods. Changes from v4 (http://lkml.org/lkml/2009/5/2/91) include: o Squeeze the size down a bit further by removing the ->completed field from struct rcu_ctrlblk. o This permits synchronize_rcu() to become the empty function. Previous concerns about rcutorture were unfounded, as rcutorture correctly handles a constant value from rcu_batches_completed() and rcu_batches_completed_bh(). Changes from v3 (http://lkml.org/lkml/2009/3/29/221) include: o Changed rcu_batches_completed(), rcu_batches_completed_bh() rcu_enter_nohz(), rcu_exit_nohz(), rcu_nmi_enter(), and rcu_nmi_exit(), to be static inlines, as suggested by David Howells. Doing this saves about 100 bytes from rcutiny.o. (The numbers between v3 and this v4 of the patch are not directly comparable, since they are against different versions of Linux.) Changes from v2 (http://lkml.org/lkml/2009/2/3/333) include: o Fix whitespace issues. o Change short-circuit "||" operator to instead be "+" in order to fix performance bug noted by "kraai" on LWN. (http://lwn.net/Articles/324348/) Changes from v1 (http://lkml.org/lkml/2009/1/13/440) include: o This version depends on EMBEDDED as well as !SMP, as suggested by Ingo. o Updated rcu_needs_cpu() to unconditionally return zero, permitting the CPU to enter dynticks-idle mode at any time. This works because callbacks can be invoked upon entry to dynticks-idle mode. o Paul is now OK with this being included, based on a poll at the Kernel Miniconf at linux.conf.au, where about ten people said that they cared about saving 900 bytes on single-CPU systems. o Applies to both mainline and tip/core/rcu. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: Josh Triplett <josh@joshtriplett.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: avi@redhat.com Cc: mtosatti@redhat.com LKML-Reference: <12565226351355-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-10-26 10:03:50 +08:00
{
synchronize_sched();
}
static inline void synchronize_rcu_bh_expedited(void)
{
synchronize_sched();
}
static inline void synchronize_sched_expedited(void)
{
synchronize_sched();
}
static inline void kfree_call_rcu(struct rcu_head *head,
rcu_callback_t func)
{
call_rcu(head, func);
}
static inline void rcu_note_context_switch(void)
rcu: Add a TINY_PREEMPT_RCU Implement a small-memory-footprint uniprocessor-only implementation of preemptible RCU. This implementation uses but a single blocked-tasks list rather than the combinatorial number used per leaf rcu_node by TREE_PREEMPT_RCU, which reduces memory consumption and greatly simplifies processing. This version also takes advantage of uniprocessor execution to accelerate grace periods in the case where there are no readers. The general design is otherwise broadly similar to that of TREE_PREEMPT_RCU. This implementation is a step towards having RCU implementation driven off of the SMP and PREEMPT kernel configuration variables, which can happen once this implementation has accumulated sufficient experience. Removed ACCESS_ONCE() from __rcu_read_unlock() and added barrier() as suggested by Steve Rostedt in order to avoid the compiler-reordering issue noted by Mathieu Desnoyers (http://lkml.org/lkml/2010/8/16/183). As can be seen below, CONFIG_TINY_PREEMPT_RCU represents almost 5Kbyte savings compared to CONFIG_TREE_PREEMPT_RCU. Of course, for non-real-time workloads, CONFIG_TINY_RCU is even better. CONFIG_TREE_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 6170 825 28 7023 kernel/rcutree.o ---- 7026 Total CONFIG_TINY_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 2081 81 8 2170 kernel/rcutiny.o ---- 2183 Total CONFIG_TINY_RCU (non-preemptible) text data bss dec filename 13 0 0 13 kernel/rcupdate.o 719 25 0 744 kernel/rcutiny.o --- 757 Total Requested-by: Loïc Minier <loic.minier@canonical.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-06-30 07:49:16 +08:00
{
rcu_sched_qs();
rcu: Add a TINY_PREEMPT_RCU Implement a small-memory-footprint uniprocessor-only implementation of preemptible RCU. This implementation uses but a single blocked-tasks list rather than the combinatorial number used per leaf rcu_node by TREE_PREEMPT_RCU, which reduces memory consumption and greatly simplifies processing. This version also takes advantage of uniprocessor execution to accelerate grace periods in the case where there are no readers. The general design is otherwise broadly similar to that of TREE_PREEMPT_RCU. This implementation is a step towards having RCU implementation driven off of the SMP and PREEMPT kernel configuration variables, which can happen once this implementation has accumulated sufficient experience. Removed ACCESS_ONCE() from __rcu_read_unlock() and added barrier() as suggested by Steve Rostedt in order to avoid the compiler-reordering issue noted by Mathieu Desnoyers (http://lkml.org/lkml/2010/8/16/183). As can be seen below, CONFIG_TINY_PREEMPT_RCU represents almost 5Kbyte savings compared to CONFIG_TREE_PREEMPT_RCU. Of course, for non-real-time workloads, CONFIG_TINY_RCU is even better. CONFIG_TREE_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 6170 825 28 7023 kernel/rcutree.o ---- 7026 Total CONFIG_TINY_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 2081 81 8 2170 kernel/rcutiny.o ---- 2183 Total CONFIG_TINY_RCU (non-preemptible) text data bss dec filename 13 0 0 13 kernel/rcupdate.o 719 25 0 744 kernel/rcutiny.o --- 757 Total Requested-by: Loïc Minier <loic.minier@canonical.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-06-30 07:49:16 +08:00
}
/*
* Take advantage of the fact that there is only one CPU, which
* allows us to ignore virtualization-based context switches.
*/
static inline void rcu_virt_note_context_switch(int cpu)
{
}
rcu: Add a TINY_PREEMPT_RCU Implement a small-memory-footprint uniprocessor-only implementation of preemptible RCU. This implementation uses but a single blocked-tasks list rather than the combinatorial number used per leaf rcu_node by TREE_PREEMPT_RCU, which reduces memory consumption and greatly simplifies processing. This version also takes advantage of uniprocessor execution to accelerate grace periods in the case where there are no readers. The general design is otherwise broadly similar to that of TREE_PREEMPT_RCU. This implementation is a step towards having RCU implementation driven off of the SMP and PREEMPT kernel configuration variables, which can happen once this implementation has accumulated sufficient experience. Removed ACCESS_ONCE() from __rcu_read_unlock() and added barrier() as suggested by Steve Rostedt in order to avoid the compiler-reordering issue noted by Mathieu Desnoyers (http://lkml.org/lkml/2010/8/16/183). As can be seen below, CONFIG_TINY_PREEMPT_RCU represents almost 5Kbyte savings compared to CONFIG_TREE_PREEMPT_RCU. Of course, for non-real-time workloads, CONFIG_TINY_RCU is even better. CONFIG_TREE_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 6170 825 28 7023 kernel/rcutree.o ---- 7026 Total CONFIG_TINY_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 2081 81 8 2170 kernel/rcutiny.o ---- 2183 Total CONFIG_TINY_RCU (non-preemptible) text data bss dec filename 13 0 0 13 kernel/rcupdate.o 719 25 0 744 kernel/rcutiny.o --- 757 Total Requested-by: Loïc Minier <loic.minier@canonical.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-06-30 07:49:16 +08:00
/*
* Return the number of grace periods started.
rcu: Add a TINY_PREEMPT_RCU Implement a small-memory-footprint uniprocessor-only implementation of preemptible RCU. This implementation uses but a single blocked-tasks list rather than the combinatorial number used per leaf rcu_node by TREE_PREEMPT_RCU, which reduces memory consumption and greatly simplifies processing. This version also takes advantage of uniprocessor execution to accelerate grace periods in the case where there are no readers. The general design is otherwise broadly similar to that of TREE_PREEMPT_RCU. This implementation is a step towards having RCU implementation driven off of the SMP and PREEMPT kernel configuration variables, which can happen once this implementation has accumulated sufficient experience. Removed ACCESS_ONCE() from __rcu_read_unlock() and added barrier() as suggested by Steve Rostedt in order to avoid the compiler-reordering issue noted by Mathieu Desnoyers (http://lkml.org/lkml/2010/8/16/183). As can be seen below, CONFIG_TINY_PREEMPT_RCU represents almost 5Kbyte savings compared to CONFIG_TREE_PREEMPT_RCU. Of course, for non-real-time workloads, CONFIG_TINY_RCU is even better. CONFIG_TREE_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 6170 825 28 7023 kernel/rcutree.o ---- 7026 Total CONFIG_TINY_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 2081 81 8 2170 kernel/rcutiny.o ---- 2183 Total CONFIG_TINY_RCU (non-preemptible) text data bss dec filename 13 0 0 13 kernel/rcupdate.o 719 25 0 744 kernel/rcutiny.o --- 757 Total Requested-by: Loïc Minier <loic.minier@canonical.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-06-30 07:49:16 +08:00
*/
static inline unsigned long rcu_batches_started(void)
rcu: Add a TINY_PREEMPT_RCU Implement a small-memory-footprint uniprocessor-only implementation of preemptible RCU. This implementation uses but a single blocked-tasks list rather than the combinatorial number used per leaf rcu_node by TREE_PREEMPT_RCU, which reduces memory consumption and greatly simplifies processing. This version also takes advantage of uniprocessor execution to accelerate grace periods in the case where there are no readers. The general design is otherwise broadly similar to that of TREE_PREEMPT_RCU. This implementation is a step towards having RCU implementation driven off of the SMP and PREEMPT kernel configuration variables, which can happen once this implementation has accumulated sufficient experience. Removed ACCESS_ONCE() from __rcu_read_unlock() and added barrier() as suggested by Steve Rostedt in order to avoid the compiler-reordering issue noted by Mathieu Desnoyers (http://lkml.org/lkml/2010/8/16/183). As can be seen below, CONFIG_TINY_PREEMPT_RCU represents almost 5Kbyte savings compared to CONFIG_TREE_PREEMPT_RCU. Of course, for non-real-time workloads, CONFIG_TINY_RCU is even better. CONFIG_TREE_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 6170 825 28 7023 kernel/rcutree.o ---- 7026 Total CONFIG_TINY_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 2081 81 8 2170 kernel/rcutiny.o ---- 2183 Total CONFIG_TINY_RCU (non-preemptible) text data bss dec filename 13 0 0 13 kernel/rcupdate.o 719 25 0 744 kernel/rcutiny.o --- 757 Total Requested-by: Loïc Minier <loic.minier@canonical.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-06-30 07:49:16 +08:00
{
return 0;
}
/*
* Return the number of bottom-half grace periods started.
rcu: Add a TINY_PREEMPT_RCU Implement a small-memory-footprint uniprocessor-only implementation of preemptible RCU. This implementation uses but a single blocked-tasks list rather than the combinatorial number used per leaf rcu_node by TREE_PREEMPT_RCU, which reduces memory consumption and greatly simplifies processing. This version also takes advantage of uniprocessor execution to accelerate grace periods in the case where there are no readers. The general design is otherwise broadly similar to that of TREE_PREEMPT_RCU. This implementation is a step towards having RCU implementation driven off of the SMP and PREEMPT kernel configuration variables, which can happen once this implementation has accumulated sufficient experience. Removed ACCESS_ONCE() from __rcu_read_unlock() and added barrier() as suggested by Steve Rostedt in order to avoid the compiler-reordering issue noted by Mathieu Desnoyers (http://lkml.org/lkml/2010/8/16/183). As can be seen below, CONFIG_TINY_PREEMPT_RCU represents almost 5Kbyte savings compared to CONFIG_TREE_PREEMPT_RCU. Of course, for non-real-time workloads, CONFIG_TINY_RCU is even better. CONFIG_TREE_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 6170 825 28 7023 kernel/rcutree.o ---- 7026 Total CONFIG_TINY_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 2081 81 8 2170 kernel/rcutiny.o ---- 2183 Total CONFIG_TINY_RCU (non-preemptible) text data bss dec filename 13 0 0 13 kernel/rcupdate.o 719 25 0 744 kernel/rcutiny.o --- 757 Total Requested-by: Loïc Minier <loic.minier@canonical.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-06-30 07:49:16 +08:00
*/
static inline unsigned long rcu_batches_started_bh(void)
{
return 0;
}
/*
* Return the number of sched grace periods started.
*/
static inline unsigned long rcu_batches_started_sched(void)
{
return 0;
}
/*
* Return the number of grace periods completed.
rcu: Add a TINY_PREEMPT_RCU Implement a small-memory-footprint uniprocessor-only implementation of preemptible RCU. This implementation uses but a single blocked-tasks list rather than the combinatorial number used per leaf rcu_node by TREE_PREEMPT_RCU, which reduces memory consumption and greatly simplifies processing. This version also takes advantage of uniprocessor execution to accelerate grace periods in the case where there are no readers. The general design is otherwise broadly similar to that of TREE_PREEMPT_RCU. This implementation is a step towards having RCU implementation driven off of the SMP and PREEMPT kernel configuration variables, which can happen once this implementation has accumulated sufficient experience. Removed ACCESS_ONCE() from __rcu_read_unlock() and added barrier() as suggested by Steve Rostedt in order to avoid the compiler-reordering issue noted by Mathieu Desnoyers (http://lkml.org/lkml/2010/8/16/183). As can be seen below, CONFIG_TINY_PREEMPT_RCU represents almost 5Kbyte savings compared to CONFIG_TREE_PREEMPT_RCU. Of course, for non-real-time workloads, CONFIG_TINY_RCU is even better. CONFIG_TREE_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 6170 825 28 7023 kernel/rcutree.o ---- 7026 Total CONFIG_TINY_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 2081 81 8 2170 kernel/rcutiny.o ---- 2183 Total CONFIG_TINY_RCU (non-preemptible) text data bss dec filename 13 0 0 13 kernel/rcupdate.o 719 25 0 744 kernel/rcutiny.o --- 757 Total Requested-by: Loïc Minier <loic.minier@canonical.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-06-30 07:49:16 +08:00
*/
static inline unsigned long rcu_batches_completed(void)
rcu: Add a TINY_PREEMPT_RCU Implement a small-memory-footprint uniprocessor-only implementation of preemptible RCU. This implementation uses but a single blocked-tasks list rather than the combinatorial number used per leaf rcu_node by TREE_PREEMPT_RCU, which reduces memory consumption and greatly simplifies processing. This version also takes advantage of uniprocessor execution to accelerate grace periods in the case where there are no readers. The general design is otherwise broadly similar to that of TREE_PREEMPT_RCU. This implementation is a step towards having RCU implementation driven off of the SMP and PREEMPT kernel configuration variables, which can happen once this implementation has accumulated sufficient experience. Removed ACCESS_ONCE() from __rcu_read_unlock() and added barrier() as suggested by Steve Rostedt in order to avoid the compiler-reordering issue noted by Mathieu Desnoyers (http://lkml.org/lkml/2010/8/16/183). As can be seen below, CONFIG_TINY_PREEMPT_RCU represents almost 5Kbyte savings compared to CONFIG_TREE_PREEMPT_RCU. Of course, for non-real-time workloads, CONFIG_TINY_RCU is even better. CONFIG_TREE_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 6170 825 28 7023 kernel/rcutree.o ---- 7026 Total CONFIG_TINY_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 2081 81 8 2170 kernel/rcutiny.o ---- 2183 Total CONFIG_TINY_RCU (non-preemptible) text data bss dec filename 13 0 0 13 kernel/rcupdate.o 719 25 0 744 kernel/rcutiny.o --- 757 Total Requested-by: Loïc Minier <loic.minier@canonical.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-06-30 07:49:16 +08:00
{
return 0;
}
/*
* Return the number of bottom-half grace periods completed.
rcu: Add a TINY_PREEMPT_RCU Implement a small-memory-footprint uniprocessor-only implementation of preemptible RCU. This implementation uses but a single blocked-tasks list rather than the combinatorial number used per leaf rcu_node by TREE_PREEMPT_RCU, which reduces memory consumption and greatly simplifies processing. This version also takes advantage of uniprocessor execution to accelerate grace periods in the case where there are no readers. The general design is otherwise broadly similar to that of TREE_PREEMPT_RCU. This implementation is a step towards having RCU implementation driven off of the SMP and PREEMPT kernel configuration variables, which can happen once this implementation has accumulated sufficient experience. Removed ACCESS_ONCE() from __rcu_read_unlock() and added barrier() as suggested by Steve Rostedt in order to avoid the compiler-reordering issue noted by Mathieu Desnoyers (http://lkml.org/lkml/2010/8/16/183). As can be seen below, CONFIG_TINY_PREEMPT_RCU represents almost 5Kbyte savings compared to CONFIG_TREE_PREEMPT_RCU. Of course, for non-real-time workloads, CONFIG_TINY_RCU is even better. CONFIG_TREE_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 6170 825 28 7023 kernel/rcutree.o ---- 7026 Total CONFIG_TINY_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 2081 81 8 2170 kernel/rcutiny.o ---- 2183 Total CONFIG_TINY_RCU (non-preemptible) text data bss dec filename 13 0 0 13 kernel/rcupdate.o 719 25 0 744 kernel/rcutiny.o --- 757 Total Requested-by: Loïc Minier <loic.minier@canonical.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-06-30 07:49:16 +08:00
*/
static inline unsigned long rcu_batches_completed_bh(void)
rcu: Add a TINY_PREEMPT_RCU Implement a small-memory-footprint uniprocessor-only implementation of preemptible RCU. This implementation uses but a single blocked-tasks list rather than the combinatorial number used per leaf rcu_node by TREE_PREEMPT_RCU, which reduces memory consumption and greatly simplifies processing. This version also takes advantage of uniprocessor execution to accelerate grace periods in the case where there are no readers. The general design is otherwise broadly similar to that of TREE_PREEMPT_RCU. This implementation is a step towards having RCU implementation driven off of the SMP and PREEMPT kernel configuration variables, which can happen once this implementation has accumulated sufficient experience. Removed ACCESS_ONCE() from __rcu_read_unlock() and added barrier() as suggested by Steve Rostedt in order to avoid the compiler-reordering issue noted by Mathieu Desnoyers (http://lkml.org/lkml/2010/8/16/183). As can be seen below, CONFIG_TINY_PREEMPT_RCU represents almost 5Kbyte savings compared to CONFIG_TREE_PREEMPT_RCU. Of course, for non-real-time workloads, CONFIG_TINY_RCU is even better. CONFIG_TREE_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 6170 825 28 7023 kernel/rcutree.o ---- 7026 Total CONFIG_TINY_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 2081 81 8 2170 kernel/rcutiny.o ---- 2183 Total CONFIG_TINY_RCU (non-preemptible) text data bss dec filename 13 0 0 13 kernel/rcupdate.o 719 25 0 744 kernel/rcutiny.o --- 757 Total Requested-by: Loïc Minier <loic.minier@canonical.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-06-30 07:49:16 +08:00
{
return 0;
}
/*
* Return the number of sched grace periods completed.
*/
static inline unsigned long rcu_batches_completed_sched(void)
rcu: Add a TINY_PREEMPT_RCU Implement a small-memory-footprint uniprocessor-only implementation of preemptible RCU. This implementation uses but a single blocked-tasks list rather than the combinatorial number used per leaf rcu_node by TREE_PREEMPT_RCU, which reduces memory consumption and greatly simplifies processing. This version also takes advantage of uniprocessor execution to accelerate grace periods in the case where there are no readers. The general design is otherwise broadly similar to that of TREE_PREEMPT_RCU. This implementation is a step towards having RCU implementation driven off of the SMP and PREEMPT kernel configuration variables, which can happen once this implementation has accumulated sufficient experience. Removed ACCESS_ONCE() from __rcu_read_unlock() and added barrier() as suggested by Steve Rostedt in order to avoid the compiler-reordering issue noted by Mathieu Desnoyers (http://lkml.org/lkml/2010/8/16/183). As can be seen below, CONFIG_TINY_PREEMPT_RCU represents almost 5Kbyte savings compared to CONFIG_TREE_PREEMPT_RCU. Of course, for non-real-time workloads, CONFIG_TINY_RCU is even better. CONFIG_TREE_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 6170 825 28 7023 kernel/rcutree.o ---- 7026 Total CONFIG_TINY_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 2081 81 8 2170 kernel/rcutiny.o ---- 2183 Total CONFIG_TINY_RCU (non-preemptible) text data bss dec filename 13 0 0 13 kernel/rcupdate.o 719 25 0 744 kernel/rcutiny.o --- 757 Total Requested-by: Loïc Minier <loic.minier@canonical.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-06-30 07:49:16 +08:00
{
return 0;
}
static inline void rcu_force_quiescent_state(void)
{
}
static inline void rcu_bh_force_quiescent_state(void)
{
}
static inline void rcu_sched_force_quiescent_state(void)
{
}
static inline void show_rcu_gp_kthreads(void)
{
}
static inline void rcu_cpu_stall_reset(void)
{
}
static inline void rcu_idle_enter(void)
{
}
static inline void rcu_idle_exit(void)
{
}
static inline void rcu_irq_enter(void)
{
}
static inline void rcu_irq_exit_irqson(void)
{
}
static inline void rcu_irq_enter_irqson(void)
{
}
static inline void rcu_irq_exit(void)
{
}
static inline void exit_rcu(void)
{
}
#ifdef CONFIG_DEBUG_LOCK_ALLOC
extern int rcu_scheduler_active __read_mostly;
void rcu_scheduler_starting(void);
#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
static inline void rcu_scheduler_starting(void)
{
}
#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE)
static inline bool rcu_is_watching(void)
{
return __rcu_is_watching();
}
#else /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
static inline bool rcu_is_watching(void)
{
return true;
}
#endif /* #else defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
static inline void rcu_all_qs(void)
{
rcu: Don't disable preemption for Tiny and Tree RCU readers Because preempt_disable() maps to barrier() for non-debug builds, it forces the compiler to spill and reload registers. Because Tree RCU and Tiny RCU now only appear in CONFIG_PREEMPT=n builds, these barrier() instances generate needless extra code for each instance of rcu_read_lock() and rcu_read_unlock(). This extra code slows down Tree RCU and bloats Tiny RCU. This commit therefore removes the preempt_disable() and preempt_enable() from the non-preemptible implementations of __rcu_read_lock() and __rcu_read_unlock(), respectively. However, for debug purposes, preempt_disable() and preempt_enable() are still invoked if CONFIG_PREEMPT_COUNT=y, because this allows detection of sleeping inside atomic sections in non-preemptible kernels. However, Tiny and Tree RCU operates by coalescing all RCU read-side critical sections on a given CPU that lie between successive quiescent states. It is therefore necessary to compensate for removing barriers from __rcu_read_lock() and __rcu_read_unlock() by adding them to a couple of the RCU functions invoked during quiescent states, namely to rcu_all_qs() and rcu_note_context_switch(). However, note that the latter is more paranoia than necessity, at least until link-time optimizations become more aggressive. This is based on an earlier patch by Paul E. McKenney, fixing a bug encountered in kernels built with CONFIG_PREEMPT=n and CONFIG_PREEMPT_COUNT=y. Signed-off-by: Boqun Feng <boqun.feng@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-07-31 07:55:38 +08:00
barrier(); /* Avoid RCU read-side critical sections leaking across. */
}
rcu: "Tiny RCU", The Bloatwatch Edition This patch is a version of RCU designed for !SMP provided for a small-footprint RCU implementation. In particular, the implementation of synchronize_rcu() is extremely lightweight and high performance. It passes rcutorture testing in each of the four relevant configurations (combinations of NO_HZ and PREEMPT) on x86. This saves about 1K bytes compared to old Classic RCU (which is no longer in mainline), and more than three kilobytes compared to Hierarchical RCU (updated to 2.6.30): CONFIG_TREE_RCU: text data bss dec filename 183 4 0 187 kernel/rcupdate.o 2783 520 36 3339 kernel/rcutree.o 3526 Total (vs 4565 for v7) CONFIG_TREE_PREEMPT_RCU: text data bss dec filename 263 4 0 267 kernel/rcupdate.o 4594 776 52 5422 kernel/rcutree.o 5689 Total (6155 for v7) CONFIG_TINY_RCU: text data bss dec filename 96 4 0 100 kernel/rcupdate.o 734 24 0 758 kernel/rcutiny.o 858 Total (vs 848 for v7) The above is for x86. Your mileage may vary on other platforms. Further compression is possible, but is being procrastinated. Changes from v7 (http://lkml.org/lkml/2009/10/9/388) o Apply Lai Jiangshan's review comments (aside from might_sleep() in synchronize_sched(), which is covered by SMP builds). o Fix up expedited primitives. Changes from v6 (http://lkml.org/lkml/2009/9/23/293). o Forward ported to put it into the 2.6.33 stream. o Added lockdep support. o Make lightweight rcu_barrier. Changes from v5 (http://lkml.org/lkml/2009/6/23/12). o Ported to latest pre-2.6.32 merge window kernel. - Renamed rcu_qsctr_inc() to rcu_sched_qs(). - Renamed rcu_bh_qsctr_inc() to rcu_bh_qs(). - Provided trivial rcu_cpu_notify(). - Provided trivial exit_rcu(). - Provided trivial rcu_needs_cpu(). - Fixed up the rcu_*_enter/exit() functions in linux/hardirq.h. o Removed the dependence on EMBEDDED, with a view to making TINY_RCU default for !SMP at some time in the future. o Added (trivial) support for expedited grace periods. Changes from v4 (http://lkml.org/lkml/2009/5/2/91) include: o Squeeze the size down a bit further by removing the ->completed field from struct rcu_ctrlblk. o This permits synchronize_rcu() to become the empty function. Previous concerns about rcutorture were unfounded, as rcutorture correctly handles a constant value from rcu_batches_completed() and rcu_batches_completed_bh(). Changes from v3 (http://lkml.org/lkml/2009/3/29/221) include: o Changed rcu_batches_completed(), rcu_batches_completed_bh() rcu_enter_nohz(), rcu_exit_nohz(), rcu_nmi_enter(), and rcu_nmi_exit(), to be static inlines, as suggested by David Howells. Doing this saves about 100 bytes from rcutiny.o. (The numbers between v3 and this v4 of the patch are not directly comparable, since they are against different versions of Linux.) Changes from v2 (http://lkml.org/lkml/2009/2/3/333) include: o Fix whitespace issues. o Change short-circuit "||" operator to instead be "+" in order to fix performance bug noted by "kraai" on LWN. (http://lwn.net/Articles/324348/) Changes from v1 (http://lkml.org/lkml/2009/1/13/440) include: o This version depends on EMBEDDED as well as !SMP, as suggested by Ingo. o Updated rcu_needs_cpu() to unconditionally return zero, permitting the CPU to enter dynticks-idle mode at any time. This works because callbacks can be invoked upon entry to dynticks-idle mode. o Paul is now OK with this being included, based on a poll at the Kernel Miniconf at linux.conf.au, where about ten people said that they cared about saving 900 bytes on single-CPU systems. o Applies to both mainline and tip/core/rcu. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: Josh Triplett <josh@joshtriplett.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: avi@redhat.com Cc: mtosatti@redhat.com LKML-Reference: <12565226351355-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-10-26 10:03:50 +08:00
#endif /* __LINUX_RCUTINY_H */