On Fri, 2014-07-04 at 09:52 +0200, Peter Zijlstra wrote: > On Thu, Jul 03, 2014 at 06:54:50PM -0700, Jason Low wrote: > > Subject: [PATCH] rwsem: In rwsem_can_spin_on_owner(), return false if no > > owner > > > > It was found that the rwsem optimistic spinning feature can potentially > > degrade > > performance when there are readers. Perf profiles indicate in some workloads > > that significant time can be spent spinning on !owner. This is because we > > don't > > set the lock owner when readers(s) obtain the rwsem. > > > > In this patch, we'll modify rwsem_can_spin_on_owner() such that we'll return > > false if there is no lock owner. The rationale is that if we just entered > > the > > slowpath, yet there is no lock owner, then there is a possibility that a > > reader > > has the lock. To be conservative, we'll avoid spinning in these situations. > > > > Dave Chinner found performance benefits with this patch in the xfs_repair > > workload, where the total run time went from approximately 4 minutes 24 > > seconds, > > down to approximately 1 minute 26 seconds with the patch. > > > > Tested-by: Dave Chinner <[email protected]> > > Signed-off-by: Jason Low <[email protected]> > > Davidlohr, you'll be running this through your AIM and other benchmarks, > I suppose?
I ran it through aim7, and as I suspected we take a performance hit with 'custom' ~-14% throughput for > 300 users (which is still overall quite higher than rwsems without opt spinning, at around ~+45%), and we actually improve a bit (~+15%) in 'disk' with >1000 users -- which afaict resembles Dave's workload a bit. So all in all I'm quite happy with this patch. Acked-by: Davidlohr Bueso <[email protected]> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
