From mboxrd@z Thu Jan 1 00:00:00 1970 From: hare@suse.de (Hannes Reinecke) Date: Tue, 9 Feb 2016 16:32:25 +0100 Subject: [RFC PATCH] dm: fix excessive dm-mq context switching In-Reply-To: <20160209145547.GA21623@redhat.com> References: <20160204135420.GA18227@redhat.com> <20160205151334.GA82754@redhat.com> <20160205180515.GA25808@redhat.com> <20160205191909.GA25982@redhat.com> <56B7659C.8040601@dev.mellanox.co.il> <56B772D6.2090403@sandisk.com> <56B77444.3030106@dev.mellanox.co.il> <56B776DE.30101@dev.mellanox.co.il> <20160207172055.GA6477@redhat.com> <56B99A49.5050400@suse.de> <20160209145547.GA21623@redhat.com> Message-ID: <56BA0689.9030007@suse.de> On 02/09/2016 03:55 PM, Mike Snitzer wrote: > On Tue, Feb 09 2016 at 2:50am -0500, > Hannes Reinecke wrote: > >> On 02/07/2016 06:20 PM, Mike Snitzer wrote: >>> On Sun, Feb 07 2016 at 11:54am -0500, >>> Sagi Grimberg 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. Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking hare at suse.de +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 N?rnberg GF: F. Imend?rffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton HRB 21284 (AG N?rnberg) From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Reinecke Subject: Re: [RFC PATCH] dm: fix excessive dm-mq context switching Date: Tue, 9 Feb 2016 16:32:25 +0100 Message-ID: <56BA0689.9030007@suse.de> References: <20160204135420.GA18227@redhat.com> <20160205151334.GA82754@redhat.com> <20160205180515.GA25808@redhat.com> <20160205191909.GA25982@redhat.com> <56B7659C.8040601@dev.mellanox.co.il> <56B772D6.2090403@sandisk.com> <56B77444.3030106@dev.mellanox.co.il> <56B776DE.30101@dev.mellanox.co.il> <20160207172055.GA6477@redhat.com> <56B99A49.5050400@suse.de> <20160209145547.GA21623@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <20160209145547.GA21623@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Mike Snitzer Cc: "axboe@kernel.dk" , "keith.busch@intel.com" , Sagi Grimberg , "linux-nvme@lists.infradead.org" , Christoph Hellwig , device-mapper development , "linux-block@vger.kernel.org" , Bart Van Assche List-Id: dm-devel.ids On 02/09/2016 03:55 PM, Mike Snitzer wrote: > On Tue, Feb 09 2016 at 2:50am -0500, > Hannes Reinecke wrote: > = >> On 02/07/2016 06:20 PM, Mike Snitzer wrote: >>> On Sun, Feb 07 2016 at 11:54am -0500, >>> Sagi Grimberg 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 fo= r in >>>>>> the perf output is whether any functions occupy more than 10% CPU ti= me. >>>>> >>>>> 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=3D= 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. Cheers, Hannes -- = Dr. Hannes Reinecke Teamlead Storage & Networking hare@suse.de +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 N=FCrnberg GF: F. Imend=F6rffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton HRB 21284 (AG N=FCrnberg)