1d2a1e5386
4 Commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
Waiman Long
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405963b6a5 |
locking/qrwlock: Don't contend with readers when setting _QW_WAITING
The current cmpxchg() loop in setting the _QW_WAITING flag for writers in queue_write_lock_slowpath() will contend with incoming readers causing possibly extra cmpxchg() operations that are wasteful. This patch changes the code to do a byte cmpxchg() to eliminate contention with new readers. A multithreaded microbenchmark running 5M read_lock/write_lock loop on a 8-socket 80-core Westmere-EX machine running 4.0 based kernel with the qspinlock patch have the following execution times (in ms) with and without the patch: With R:W ratio = 5:1 Threads w/o patch with patch % change ------- --------- ---------- -------- 2 990 895 -9.6% 3 2136 1912 -10.5% 4 3166 2830 -10.6% 5 3953 3629 -8.2% 6 4628 4405 -4.8% 7 5344 5197 -2.8% 8 6065 6004 -1.0% 9 6826 6811 -0.2% 10 7599 7599 0.0% 15 9757 9766 +0.1% 20 13767 13817 +0.4% With small number of contending threads, this patch can improve locking performance by up to 10%. With more contending threads, however, the gain diminishes. 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: Arnd Bergmann <arnd@arndb.de> Cc: Borislav Petkov <bp@alien8.de> Cc: Douglas Hatch <doug.hatch@hp.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@hp.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1433863153-30722-3-git-send-email-Waiman.Long@hp.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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Waiman Long
|
c7114b4e6c |
locking/qrwlock: Rename QUEUE_RWLOCK to QUEUED_RWLOCKS
To be consistent with the queued spinlocks which use CONFIG_QUEUED_SPINLOCKS config parameter, the one for the queued rwlocks is now renamed to CONFIG_QUEUED_RWLOCKS. Signed-off-by: Waiman Long <Waiman.Long@hp.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Douglas Hatch <doug.hatch@hp.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Scott J Norton <scott.norton@hp.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1431367031-36697-1-git-send-email-Waiman.Long@hp.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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Davidlohr Bueso
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3a6bfbc91d |
arch, locking: Ciao arch_mutex_cpu_relax()
The arch_mutex_cpu_relax() function, introduced by
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Waiman Long
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70af2f8a4f |
locking/rwlocks: Introduce 'qrwlocks' - fair, queued rwlocks
This rwlock uses the arch_spin_lock_t as a waitqueue, and assuming the arch_spin_lock_t is a fair lock (ticket,mcs etc..) the resulting rwlock is a fair lock. It fits in the same 8 bytes as the regular rwlock_t by folding the reader and writer count into a single integer, using the remaining 4 bytes for the arch_spinlock_t. Architectures that can single-copy adress bytes can optimize queue_write_unlock() with a 0 write to the LSB (the write count). Performance as measured by Davidlohr Bueso (rwlock_t -> qrwlock_t): +--------------+-------------+---------------+ | Workload | #users | delta | +--------------+-------------+---------------+ | alltests | > 1400 | -4.83% | | custom | 0-100,> 100 | +1.43%,-1.57% | | high_systime | > 1000 | -2.61 | | shared | all | +0.32 | +--------------+-------------+---------------+ http://www.stgolabs.net/qrwlock-stuff/aim7-results-vs-rwsem_optsin/ Signed-off-by: Waiman Long <Waiman.Long@hp.com> [peterz: near complete rewrite] Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: "Paul E.McKenney" <paulmck@linux.vnet.ibm.com> Cc: linux-arch@vger.kernel.org Cc: linux-kernel@vger.kernel.org Link: http://lkml.kernel.org/n/tip-gac1nnl3wvs2ij87zv2xkdzq@git.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org> |