On Tue, Feb 09 2016 at 10:32am -0500, Hannes Reinecke <hare@xxxxxxx> wrote: > On 02/09/2016 03:55 PM, Mike Snitzer wrote: > > On Tue, Feb 09 2016 at 2:50am -0500, > > Hannes Reinecke <hare@xxxxxxx> wrote: > > > >> On 02/07/2016 06:20 PM, Mike Snitzer wrote: > >>> On Sun, Feb 07 2016 at 11:54am -0500, > >>> Sagi Grimberg <sagig@xxxxxxxxxxxxxxxxxx> wrote: > >>> > >>>> > >>>>>> If so, can you check with e.g. > >>>>>> perf record -ags -e LLC-load-misses sleep 10 && perf report whether this > >>>>>> workload triggers perhaps lock contention ? What you need to look for in > >>>>>> the perf output is whether any functions occupy more than 10% CPU time. > >>>>> > >>>>> I will, thanks for the tip! > >>>> > >>>> The perf report is very similar to the one that started this effort.. > >>>> > >>>> I'm afraid we'll need to resolve the per-target m->lock in order > >>>> to scale with NUMA... > >>> > >>> Could be. Just for testing, you can try the 2 topmost commits I've put > >>> here (once applied both __multipath_map and multipath_busy won't have > >>> _any_ locking.. again, very much test-only): > >>> > >>> http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/log/?h=devel2 > >>> > >> So, I gave those patches a spin. > >> Sad to say, they do _not_ resolve the issue fully. > >> > >> My testbed (2 paths per LUN, 40 CPUs, 4 cores) yields 505k IOPs with > >> those patches. > > > > That isn't a surprise. We knew the m->lock spinlock contention to be a > > problem. And NUMA makes it even worse. > > > >> Using a single path (without those patches, but still running > >> multipath on top of that path) the same testbed yields 550k IOPs. > >> Which very much smells like a lock contention ... > >> We do get a slight improvement, though; without those patches I > >> could only get about 350k IOPs. But still, I would somehow expect 2 > >> paths to be faster than just one .. > > > > https://www.redhat.com/archives/dm-devel/2016-February/msg00036.html > > > > hint hint... > > > I hoped they wouldn't be needed with your patches. > Plus perf revealed that I first need to address a spinlock > contention in the lpfc driver before that even would make sense. > > So more debugging to follow. OK, I took a crack at embracing RCU. Only slightly better performance on my single NUMA node testbed. (But I'll have to track down a system with multiple NUMA nodes to do any justice to the next wave of this optimization effort) This RCU work is very heavy-handed and way too fiddley (there could easily be bugs). Anyway, please see: http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/commit/?h=devel2&id=d80a7e4f8b5be9c81e4d452137623b003fa64745 But this might give you something to build on to arrive at something more scalable? Mike -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
