19 Commits
| Author | SHA1 | Message | Date |
|---|---|---|---|
Arnd Bergmann
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f44ca0871b |
qspinlock: use signed temporaries for cmpxchg
When building with W=2, the build log is flooded with
include/asm-generic/qrwlock.h:65:56: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]
include/asm-generic/qrwlock.h:92:53: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]
include/asm-generic/qspinlock.h:68:55: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]
include/asm-generic/qspinlock.h:82:52: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]
The atomics are built on top of signed integers, but the caller
doesn't actually care. Just use signed types as well.
Fixes:
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Linus Torvalds
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25d8d4eeca |
powerpc updates for 5.9
- Add support for (optionally) using queued spinlocks & rwlocks.
- Support for a new faster system call ABI using the scv instruction on Power9
or later.
- Drop support for the PROT_SAO mmap/mprotect flag as it will be unsupported on
Power10 and future processors, leaving us with no way to implement the
functionality it requests. This risks breaking userspace, though we believe
it is unused in practice.
- A bug fix for, and then the removal of, our custom stack expansion checking.
We now allow stack expansion up to the rlimit, like other architectures.
- Remove the remnants of our (previously disabled) topology update code, which
tried to react to NUMA layout changes on virtualised systems, but was prone
to crashes and other problems.
- Add PMU support for Power10 CPUs.
- A change to our signal trampoline so that we don't unbalance the link stack
(branch return predictor) in the signal delivery path.
- Lots of other cleanups, refactorings, smaller features and so on as usual.
Thanks to:
Abhishek Goel, Alastair D'Silva, Alexander A. Klimov, Alexey Kardashevskiy,
Alistair Popple, Andrew Donnellan, Aneesh Kumar K.V, Anju T Sudhakar, Anton
Blanchard, Arnd Bergmann, Athira Rajeev, Balamuruhan S, Bharata B Rao, Bill
Wendling, Bin Meng, Cédric Le Goater, Chris Packham, Christophe Leroy,
Christoph Hellwig, Daniel Axtens, Dan Williams, David Lamparter, Desnes A.
Nunes do Rosario, Erhard F., Finn Thain, Frederic Barrat, Ganesh Goudar,
Gautham R. Shenoy, Geoff Levand, Greg Kurz, Gustavo A. R. Silva, Hari Bathini,
Harish, Imre Kaloz, Joel Stanley, Joe Perches, John Crispin, Jordan Niethe,
Kajol Jain, Kamalesh Babulal, Kees Cook, Laurent Dufour, Leonardo Bras, Li
RongQing, Madhavan Srinivasan, Mahesh Salgaonkar, Mark Cave-Ayland, Michal
Suchanek, Milton Miller, Mimi Zohar, Murilo Opsfelder Araujo, Nathan
Chancellor, Nathan Lynch, Naveen N. Rao, Nayna Jain, Nicholas Piggin, Oliver
O'Halloran, Palmer Dabbelt, Pedro Miraglia Franco de Carvalho, Philippe
Bergheaud, Pingfan Liu, Pratik Rajesh Sampat, Qian Cai, Qinglang Miao, Randy
Dunlap, Ravi Bangoria, Sachin Sant, Sam Bobroff, Sandipan Das, Santosh
Sivaraj, Satheesh Rajendran, Shirisha Ganta, Sourabh Jain, Srikar Dronamraju,
Stan Johnson, Stephen Rothwell, Thadeu Lima de Souza Cascardo, Thiago Jung
Bauermann, Tom Lane, Vaibhav Jain, Vladis Dronov, Wei Yongjun, Wen Xiong,
YueHaibing.
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Merge tag 'powerpc-5.9-1' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux
Pull powerpc updates from Michael Ellerman:
- Add support for (optionally) using queued spinlocks & rwlocks.
- Support for a new faster system call ABI using the scv instruction on
Power9 or later.
- Drop support for the PROT_SAO mmap/mprotect flag as it will be
unsupported on Power10 and future processors, leaving us with no way
to implement the functionality it requests. This risks breaking
userspace, though we believe it is unused in practice.
- A bug fix for, and then the removal of, our custom stack expansion
checking. We now allow stack expansion up to the rlimit, like other
architectures.
- Remove the remnants of our (previously disabled) topology update
code, which tried to react to NUMA layout changes on virtualised
systems, but was prone to crashes and other problems.
- Add PMU support for Power10 CPUs.
- A change to our signal trampoline so that we don't unbalance the link
stack (branch return predictor) in the signal delivery path.
- Lots of other cleanups, refactorings, smaller features and so on as
usual.
Thanks to: Abhishek Goel, Alastair D'Silva, Alexander A. Klimov, Alexey
Kardashevskiy, Alistair Popple, Andrew Donnellan, Aneesh Kumar K.V, Anju
T Sudhakar, Anton Blanchard, Arnd Bergmann, Athira Rajeev, Balamuruhan
S, Bharata B Rao, Bill Wendling, Bin Meng, Cédric Le Goater, Chris
Packham, Christophe Leroy, Christoph Hellwig, Daniel Axtens, Dan
Williams, David Lamparter, Desnes A. Nunes do Rosario, Erhard F., Finn
Thain, Frederic Barrat, Ganesh Goudar, Gautham R. Shenoy, Geoff Levand,
Greg Kurz, Gustavo A. R. Silva, Hari Bathini, Harish, Imre Kaloz, Joel
Stanley, Joe Perches, John Crispin, Jordan Niethe, Kajol Jain, Kamalesh
Babulal, Kees Cook, Laurent Dufour, Leonardo Bras, Li RongQing, Madhavan
Srinivasan, Mahesh Salgaonkar, Mark Cave-Ayland, Michal Suchanek, Milton
Miller, Mimi Zohar, Murilo Opsfelder Araujo, Nathan Chancellor, Nathan
Lynch, Naveen N. Rao, Nayna Jain, Nicholas Piggin, Oliver O'Halloran,
Palmer Dabbelt, Pedro Miraglia Franco de Carvalho, Philippe Bergheaud,
Pingfan Liu, Pratik Rajesh Sampat, Qian Cai, Qinglang Miao, Randy
Dunlap, Ravi Bangoria, Sachin Sant, Sam Bobroff, Sandipan Das, Santosh
Sivaraj, Satheesh Rajendran, Shirisha Ganta, Sourabh Jain, Srikar
Dronamraju, Stan Johnson, Stephen Rothwell, Thadeu Lima de Souza
Cascardo, Thiago Jung Bauermann, Tom Lane, Vaibhav Jain, Vladis Dronov,
Wei Yongjun, Wen Xiong, YueHaibing.
* tag 'powerpc-5.9-1' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux: (337 commits)
selftests/powerpc: Fix pkey syscall redefinitions
powerpc: Fix circular dependency between percpu.h and mmu.h
powerpc/powernv/sriov: Fix use of uninitialised variable
selftests/powerpc: Skip vmx/vsx/tar/etc tests on older CPUs
powerpc/40x: Fix assembler warning about r0
powerpc/papr_scm: Add support for fetching nvdimm 'fuel-gauge' metric
powerpc/papr_scm: Fetch nvdimm performance stats from PHYP
cpuidle: pseries: Fixup exit latency for CEDE(0)
cpuidle: pseries: Add function to parse extended CEDE records
cpuidle: pseries: Set the latency-hint before entering CEDE
selftests/powerpc: Fix online CPU selection
powerpc/perf: Consolidate perf_callchain_user_[64|32]()
powerpc/pseries/hotplug-cpu: Remove double free in error path
powerpc/pseries/mobility: Add pr_debug() for device tree changes
powerpc/pseries/mobility: Set pr_fmt()
powerpc/cacheinfo: Warn if cache object chain becomes unordered
powerpc/cacheinfo: Improve diagnostics about malformed cache lists
powerpc/cacheinfo: Use name@unit instead of full DT path in debug messages
powerpc/cacheinfo: Set pr_fmt()
powerpc: fix function annotations to avoid section mismatch warnings with gcc-10
...
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Herbert Xu
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459e39538e |
locking/qspinlock: Do not include atomic.h from qspinlock_types.h
This patch breaks a header loop involving qspinlock_types.h. The issue is that qspinlock_types.h includes atomic.h, which then eventually includes kernel.h which could lead back to the original file via spinlock_types.h. As ATOMIC_INIT is now defined by linux/types.h, there is no longer any need to include atomic.h from qspinlock_types.h. This also allows the CONFIG_PARAVIRT hack to be removed since it was trying to prevent exactly this loop. Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Waiman Long <longman@redhat.com> Link: https://lkml.kernel.org/r/20200729123316.GC7047@gondor.apana.org.au |
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Nicholas Piggin
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20c0e8269e |
powerpc/pseries: Implement paravirt qspinlocks for SPLPAR
This implements the generic paravirt qspinlocks using H_PROD and H_CONFER to kick and wait. This uses an un-directed yield to any CPU rather than the directed yield to a pre-empted lock holder that paravirtualised simple spinlocks use, that requires no kick hcall. This is something that could be investigated and improved in future. Performance results can be found in the commit which added queued spinlocks. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Waiman Long <longman@redhat.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20200724131423.1362108-5-npiggin@gmail.com |
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Nicholas Piggin
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aa65ff6b18 |
powerpc/64s: Implement queued spinlocks and rwlocks
These have shown significantly improved performance and fairness when spinlock contention is moderate to high on very large systems. With this series including subsequent patches, on a 16 socket 1536 thread POWER9, a stress test such as same-file open/close from all CPUs gets big speedups, 11620op/s aggregate with simple spinlocks vs 384158op/s (33x faster), where the difference in throughput between the fastest and slowest thread goes from 7x to 1.4x. Thanks to the fast path being identical in terms of atomics and barriers (after a subsequent optimisation patch), single threaded performance is not changed (no measurable difference). On smaller systems, performance and fairness seems to be generally improved. Using dbench on tmpfs as a test (that starts to run into kernel spinlock contention), a 2-socket OpenPOWER POWER9 system was tested with bare metal and KVM guest configurations. Results can be found here: https://github.com/linuxppc/issues/issues/305#issuecomment-663487453 Observations are: - Queued spinlocks are equal when contention is insignificant, as expected and as measured with microbenchmarks. - When there is contention, on bare metal queued spinlocks have better throughput and max latency at all points. - When virtualised, queued spinlocks are slightly worse approaching peak throughput, but significantly better throughput and max latency at all points beyond peak, until queued spinlock maximum latency rises when clients are 2x vCPUs. The regressions haven't been analysed very well yet, there are a lot of things that can be tuned, particularly the paravirtualised locking, but the numbers already look like a good net win even on relatively small systems. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Waiman Long <longman@redhat.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20200724131423.1362108-4-npiggin@gmail.com |
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Thomas Gleixner
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c942fddf87 |
treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157
Based on 3 normalized pattern(s): 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 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 [author] [kishon] [vijay] [abraham] [i] [kishon]@[ti] [com] 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 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 [author] [graeme] [gregory] [gg]@[slimlogic] [co] [uk] [author] [kishon] [vijay] [abraham] [i] [kishon]@[ti] [com] [based] [on] [twl6030]_[usb] [c] [author] [hema] [hk] [hemahk]@[ti] [com] 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 extracted by the scancode license scanner the SPDX license identifier GPL-2.0-or-later has been chosen to replace the boilerplate/reference in 1105 file(s). Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Allison Randal <allison@lohutok.net> Reviewed-by: Richard Fontana <rfontana@redhat.com> Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org> Cc: linux-spdx@vger.kernel.org Link: https://lkml.kernel.org/r/20190527070033.202006027@linutronix.de Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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Matthew Wilcox
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27df89689e |
locking/spinlocks: Remove an instruction from spin and write locks
Both spin locks and write locks currently do: f0 0f b1 17 lock cmpxchg %edx,(%rdi) 85 c0 test %eax,%eax 75 05 jne [slowpath] This 'test' insn is superfluous; the cmpxchg insn sets the Z flag appropriately. Peter pointed out that using atomic_try_cmpxchg_acquire() will let the compiler know this is true. Comparing before/after disassemblies show the only effect is to remove this insn. Take this opportunity to make the spin & write lock code resemble each other more closely and have similar likely() hints. Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Matthew Wilcox <willy@infradead.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Will Deacon <will.deacon@arm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Waiman Long <longman@redhat.com> Link: http://lkml.kernel.org/r/20180820162639.GC25153@bombadil.infradead.org Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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Andrea Parri
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1362ae43c5 |
locking/spinlocks: Clean up comment and #ifndef for {,queued_}spin_is_locked()
Removes "#ifndef queued_spin_is_locked" from the generic code: this is unused and it's reasonable to conclude that it will continue to be unused. Also removes the comment about spin_is_locked() from mutex_is_locked(): the comment remains valid but not particularly useful. Suggested-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Will Deacon <will.deacon@arm.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: akiyks@gmail.com Cc: boqun.feng@gmail.com Cc: dhowells@redhat.com Cc: j.alglave@ucl.ac.uk Cc: linux-arch@vger.kernel.org Cc: luc.maranget@inria.fr Cc: npiggin@gmail.com Cc: parri.andrea@gmail.com Cc: stern@rowland.harvard.edu Link: http://lkml.kernel.org/r/1526338889-7003-3-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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Will Deacon
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626e5fbc14 |
locking/qspinlock: Use smp_store_release() in queued_spin_unlock()
A qspinlock can be unlocked simply by writing zero to the locked byte. This can be implemented in the generic code, so do that and remove the arch-specific override for x86 in the !PV case. Signed-off-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Waiman Long <longman@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: boqun.feng@gmail.com Cc: linux-arm-kernel@lists.infradead.org Cc: paulmck@linux.vnet.ibm.com Link: http://lkml.kernel.org/r/1524738868-31318-11-git-send-email-will.deacon@arm.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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Will Deacon
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a4c1887d4c |
locking/arch: Remove dummy arch_{read,spin,write}_lock_flags() implementations
The arch_{read,spin,write}_lock_flags() macros are simply mapped to the
non-flags versions by the majority of architectures, so do this in core
code and remove the dummy implementations. Also remove the implementation
in spinlock_up.h, since all callers of do_raw_spin_lock_flags() call
local_irq_save(flags) anyway.
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1507055129-12300-4-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Paul E. McKenney
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d3a024abbc |
locking: Remove spin_unlock_wait() generic definitions
There is no agreed-upon definition of spin_unlock_wait()'s semantics, and it appears that all callers could do just as well with a lock/unlock pair. This commit therefore removes spin_unlock_wait() and related definitions from core code. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Alan Stern <stern@rowland.harvard.edu> Cc: Andrea Parri <parri.andrea@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> |
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Pan Xinhui
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ca50e426f9 |
locking/qspinlock: Use atomic_sub_return_release() in queued_spin_unlock()
The existing version uses a heavy barrier while only release semantics is required. So use atomic_sub_return_release() instead. Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: arnd@arndb.de Cc: waiman.long@hp.com Link: http://lkml.kernel.org/r/1464943094-3129-1-git-send-email-xinhui.pan@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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Peter Zijlstra
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2c61002271 |
locking/qspinlock: Fix spin_unlock_wait() some more
While this prior commit: |
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Peter Zijlstra
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54cf809b95 |
locking,qspinlock: Fix spin_is_locked() and spin_unlock_wait()
Similar to commits: |
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Dan Streetman
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b82e530290 |
locking/qspinlock: Move __ARCH_SPIN_LOCK_UNLOCKED to qspinlock_types.h
Move the __ARCH_SPIN_LOCK_UNLOCKED definition from qspinlock.h into qspinlock_types.h. The definition of __ARCH_SPIN_LOCK_UNLOCKED comes from the build arch's include files; but on x86 when CONFIG_QUEUED_SPINLOCKS=y, it just it's defined in asm-generic/qspinlock.h. In most cases, this doesn't matter because linux/spinlock.h includes asm/spinlock.h, which for x86 includes asm-generic/qspinlock.h. However, any code that only includes linux/mutex.h will break, because it only includes asm/spinlock_types.h. For example, this breaks systemtap, which only includes mutex.h. Signed-off-by: Dan Streetman <dan.streetman@canonical.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Waiman Long <Waiman.Long@hpe.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Dan Streetman <ddstreet@ieee.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1455907767-17821-1-git-send-email-dan.streetman@canonical.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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Waiman Long
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64d816cba0 |
locking/qspinlock: Use _acquire/_release() versions of cmpxchg() & xchg()
This patch replaces the cmpxchg() and xchg() calls in the native qspinlock code with the more relaxed _acquire or _release versions of those calls to enable other architectures to adopt queued spinlocks with less memory barrier performance overhead. Signed-off-by: Waiman Long <Waiman.Long@hpe.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Douglas Hatch <doug.hatch@hpe.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Scott J Norton <scott.norton@hpe.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1447114167-47185-2-git-send-email-Waiman.Long@hpe.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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Peter Zijlstra
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43b3f02899 |
locking/qspinlock/x86: Fix performance regression under unaccelerated VMs
Dave ran into horrible performance on a VM without PARAVIRT_SPINLOCKS set and Linus noted that the test-and-set implementation was retarded. One should spin on the variable with a load, not a RMW. While there, remove 'queued' from the name, as the lock isn't queued at all, but a simple test-and-set. Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Reported-by: Dave Chinner <david@fromorbit.com> Tested-by: Dave Chinner <david@fromorbit.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Waiman Long <Waiman.Long@hp.com> Cc: stable@vger.kernel.org # v4.2+ Link: http://lkml.kernel.org/r/20150904152523.GR18673@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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Peter Zijlstra (Intel)
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2aa79af642 |
locking/qspinlock: Revert to test-and-set on hypervisors
When we detect a hypervisor (!paravirt, see qspinlock paravirt support patches), revert to a simple test-and-set lock to avoid the horrors of queue preemption. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Waiman Long <Waiman.Long@hp.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Daniel J Blueman <daniel@numascale.com> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Douglas Hatch <doug.hatch@hp.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Paolo Bonzini <paolo.bonzini@gmail.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> Cc: Rik van Riel <riel@redhat.com> Cc: Scott J Norton <scott.norton@hp.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: virtualization@lists.linux-foundation.org Cc: xen-devel@lists.xenproject.org Link: http://lkml.kernel.org/r/1429901803-29771-8-git-send-email-Waiman.Long@hp.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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Waiman Long
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a33fda35e3 |
locking/qspinlock: Introduce a simple generic 4-byte queued spinlock
This patch introduces a new generic queued spinlock implementation that can serve as an alternative to the default ticket spinlock. Compared with the ticket spinlock, this queued spinlock should be almost as fair as the ticket spinlock. It has about the same speed in single-thread and it can be much faster in high contention situations especially when the spinlock is embedded within the data structure to be protected. Only in light to moderate contention where the average queue depth is around 1-3 will this queued spinlock be potentially a bit slower due to the higher slowpath overhead. This queued spinlock is especially suit to NUMA machines with a large number of cores as the chance of spinlock contention is much higher in those machines. The cost of contention is also higher because of slower inter-node memory traffic. Due to the fact that spinlocks are acquired with preemption disabled, the process will not be migrated to another CPU while it is trying to get a spinlock. Ignoring interrupt handling, a CPU can only be contending in one spinlock at any one time. Counting soft IRQ, hard IRQ and NMI, a CPU can only have a maximum of 4 concurrent lock waiting activities. By allocating a set of per-cpu queue nodes and used them to form a waiting queue, we can encode the queue node address into a much smaller 24-bit size (including CPU number and queue node index) leaving one byte for the lock. Please note that the queue node is only needed when waiting for the lock. Once the lock is acquired, the queue node can be released to be used later. Signed-off-by: Waiman Long <Waiman.Long@hp.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Daniel J Blueman <daniel@numascale.com> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Douglas Hatch <doug.hatch@hp.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Paolo Bonzini <paolo.bonzini@gmail.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> Cc: Rik van Riel <riel@redhat.com> Cc: Scott J Norton <scott.norton@hp.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: virtualization@lists.linux-foundation.org Cc: xen-devel@lists.xenproject.org Link: http://lkml.kernel.org/r/1429901803-29771-2-git-send-email-Waiman.Long@hp.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |