OpenCloudOS-Kernel/kernel/sched
Vincent Guittot 05bfb65f52 sched: Remove a wake_affine() condition
In wake_affine() I have tried to understand the meaning of the condition:

 (this_load <= load &&
  this_load + target_load(prev_cpu, idx) <= tl_per_task)

but I failed to find a use case that can take advantage of it and I haven't
found clear description in the previous commit's log.

Futhermore, the comment of the condition refers to the task_hot function that
was used before being replaced by the current condition:

/*
 * This domain has SD_WAKE_AFFINE and
 * p is cache cold in this domain, and
 * there is no bad imbalance.
 */

If we look more deeply the below condition:

 this_load + target_load(prev_cpu, idx) <= tl_per_task

When sync is clear, we have:

 tl_per_task = runnable_load_avg / nr_running
 this_load = max(runnable_load_avg, cpuload[idx])
 target_load =  max(runnable_load_avg', cpuload'[idx])

It implies that runnable_load_avg == 0 and nr_running <= 1 in order to match the
condition. This implies that runnable_load_avg == 0 too because of the
condition: this_load <= load.

but if this _load is null, 'balanced' is already set and the test is redundant.

If sync is set, it's not as straight forward as above (especially if cgroup
are involved) but the policy should be similar as we have removed a task that's
going to sleep in order to get a more accurate load and this_load values.

The current conclusion is that these additional condition don't give any benefit
so we can remove them.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: preeti@linux.vnet.ibm.com
Cc: riel@redhat.com
Cc: Morten.Rasmussen@arm.com
Cc: efault@gmx.de
Cc: nicolas.pitre@linaro.org
Cc: daniel.lezcano@linaro.org
Cc: dietmar.eggemann@arm.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1409051215-16788-3-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2014-09-19 12:35:25 +02:00
..
Makefile sched/idle: Move cpu/idle.c to sched/idle.c 2014-02-11 09:58:30 +01:00
auto_group.c sched: Change autogroup_move_group() to use for_each_thread() 2014-08-20 09:47:18 +02:00
auto_group.h Revert "sched/autogroup: Fix crash on reboot when autogroup is disabled" 2012-12-11 10:23:45 +01:00
clock.c kernel: use macros from compiler.h instead of __attribute__((...)) 2014-04-07 16:36:11 -07:00
completion.c sched: Move completion code from core.c to completion.c 2013-11-06 07:49:19 +01:00
core.c sched: Add default-disabled option to BUG() when stack end location is overwritten 2014-09-19 12:35:24 +02:00
cpuacct.c cgroup: rename cgroup_subsys->base_cftypes to ->legacy_cftypes 2014-07-15 11:05:09 -04:00
cpuacct.h sched/cpuacct: Initialize root cpuacct earlier 2013-04-10 13:54:20 +02:00
cpudeadline.c sched/deadline: Replace NR_CPUS arrays 2014-05-22 10:21:28 +02:00
cpudeadline.h sched/deadline: Replace NR_CPUS arrays 2014-05-22 10:21:28 +02:00
cpupri.c Merge commit '3cf2f34' into sched/core, to fix build error 2014-06-12 13:46:37 +02:00
cpupri.h sched/cpupri: Replace NR_CPUS arrays 2014-05-22 10:21:29 +02:00
cputime.c sched, time: Fix lock inversion in thread_group_cputime() 2014-09-19 12:35:17 +02:00
deadline.c sched/dl: Simplify pick_dl_task() 2014-09-19 12:35:20 +02:00
debug.c sched: s/do_each_thread/for_each_process_thread/ in debug.c 2014-08-20 09:47:17 +02:00
fair.c sched: Remove a wake_affine() condition 2014-09-19 12:35:25 +02:00
features.h sched: Rename capacity related flags 2014-06-05 11:52:32 +02:00
idle.c ACPI and power management updates for 3.17-rc1 2014-08-06 20:34:19 -07:00
idle_task.c sched: Transform resched_task() into resched_curr() 2014-07-16 13:38:19 +02:00
proc.c cpuidle: menu: Lookup CPU runqueues less 2014-08-06 21:17:45 +02:00
rt.c sched/rt: Remove useless if from cleanup pick_next_task_rt() 2014-09-19 12:35:20 +02:00
sched.h sched: Teach scheduler to understand TASK_ON_RQ_MIGRATING state 2014-08-20 14:53:00 +02:00
stats.c kernel: audit/fix non-modular users of module_init in core code 2014-04-03 16:21:07 -07:00
stats.h sched: Micro-optimize by dropping unnecessary task_rq() calls 2013-09-25 13:51:06 +02:00
stop_task.c sched: Add wrapper for checking task_struct::on_rq 2014-08-20 14:52:59 +02:00
wait.c sched: Allow wait_on_bit_action() functions to support a timeout 2014-07-16 15:10:41 +02:00