On Thu, Jun 25, 2015 at 09:33:36PM +0100, Waiman Long wrote: > 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@xxxxxx> > > 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. Sure, I'll rework my series when -rc1 lands and take this change into account. Will -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
