On Fri, Jul 04, 2014 at 12:06:19AM -0700, Jason Low wrote: > On Fri, 2014-07-04 at 16:13 +1000, Dave Chinner wrote: > > On Thu, Jul 03, 2014 at 06:54:50PM -0700, Jason Low wrote: > > > On Thu, 2014-07-03 at 18:46 -0700, Jason Low wrote: > > > > On Fri, 2014-07-04 at 11:01 +1000, Dave Chinner wrote: > > > > > > > > FWIW, the rwsems in the struct xfs_inode are often heavily > > > > > read/write contended, so there are lots of IO related workloads that > > > > > are going to regress on XFS without this optimisation... > > > > > > > > > > Anyway, consider the patch: > > > > > > > > > > Tested-by: Dave Chinner <dchin...@redhat.com> > > > > > > > > Hi Dave, > > > > > > > > Thanks for testing. I'll update the patch with an actual changelog. > > > > > > --- > > > 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. > > > > I don't think you're being a little shifty with the truth here. > > There's no "potentially degrade performance" here - I reported a > > massive real world performance regression caused by optimistic > > spinning. > > Sure, though I mainly used the word "potentially" since there can be > other workloads out there where spinning even when readers have the lock > is a positive thing. > > And agreed that the changelog can be modified to try reflecting more on > it being a "regression fix" then a "new performance" addition. > > So how about the following?
Looks good. Thanks! -Dave. -- Dave Chinner da...@fromorbit.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
