Messages in this thread | | | Date | Thu, 25 Jun 2015 16:33:36 -0400 | From | Waiman Long <> | Subject | Re: [PATCH v5 3/3] locking/qrwlock: Don't contend with readers when setting _QW_WAITING |
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On 06/25/2015 02:35 PM, Peter Zijlstra wrote: > On Fri, Jun 19, 2015 at 11:50:02AM -0400, Waiman Long wrote: >> 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. >> >> With the extended qrwlock structure defined in asm-generic/qrwlock, >> the queue_write_unlock() function is also simplified to a >> smp_store_release() call. >> >> Signed-off-by: Waiman Long<Waiman.Long@hp.com> > This one does not in fact apply, seeing how I applied a previous > version. > > Please send an incremental patch if you still want to change things to > this form.
I saw that Ingo has merged a previous version of the patch. I am fine with that version. As Will is working on a qrwlock patch to enable ARM to use it, I will let him make the structure move to qrwlock.h if he choose to do so.
Cheers, Longman
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