From: Long Li <longli@microsoft.com> To: Ming Lei <ming.lei@redhat.com> Cc: Keith Busch <kbusch@kernel.org>, Jens Axboe <axboe@fb.com>, Christoph Hellwig <hch@lst.de>, "linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>, Sagi Grimberg <sagi@grimberg.me> Subject: RE: [PATCH 2/2] nvme-pci: poll IO after batch submission for multi-mapping queue Date: Tue, 12 Nov 2019 21:20:27 +0000 Message-ID: <CY4PR21MB0741BB1F48C64613BF6E45F6CE770@CY4PR21MB0741.namprd21.prod.outlook.com> (raw) In-Reply-To: <20191112023920.GD15079@ming.t460p> >Subject: Re: [PATCH 2/2] nvme-pci: poll IO after batch submission for multi- >mapping queue > >On Tue, Nov 12, 2019 at 12:33:50AM +0000, Long Li wrote: >> >From: Christoph Hellwig <hch@lst.de> >> >Sent: Monday, November 11, 2019 12:45 PM >> >To: Ming Lei <ming.lei@redhat.com> >> >Cc: linux-nvme@lists.infradead.org; Keith Busch <kbusch@kernel.org>; >> >Jens Axboe <axboe@fb.com>; Christoph Hellwig <hch@lst.de>; Sagi >> >Grimberg <sagi@grimberg.me>; Long Li <longli@microsoft.com> >> >Subject: Re: [PATCH 2/2] nvme-pci: poll IO after batch submission for >> >multi- mapping queue >> > >> >On Fri, Nov 08, 2019 at 11:55:08AM +0800, Ming Lei wrote: >> >> f9dde187fa92("nvme-pci: remove cq check after submission") removes >> >> cq check after submission, this change actually causes performance >> >> regression on some NVMe drive in which single nvmeq handles >> >> requests originated from more than one blk-mq sw queues(call it >> >> multi-mapping queue). >> > >> >> Follows test result done on Azure L80sv2 guest with NVMe drive( >> >> Microsoft Corporation Device b111). This guest has 80 CPUs and 10 >> >> numa nodes, and each NVMe drive supports 8 hw queues. >> > >> >Have you actually seen this on a real nvme drive as well? >> > >> >Note that it is kinda silly to limit queues like that in VMs, so I >> >really don't think we should optimize the driver for this particular case. >> >> I tested on an Azure L80s_v2 VM with newer Samsung P983 NVMe SSD >(with 32 hardware queues). Tests also showed soft lockup when 32 queues >are shared by 80 CPUs. >> > >BTW, do you see if this simple change makes a difference? Yes, I can confirm the patch fixed lockup on this VM configuration. There is also no performance regression. > >> The issue will likely show up if the number of NVMe hardware queues is >> less than the number of CPUs. I think this may be a likely >> configuration on a very large system. (e.g. the largest VM on Azure >> has 416 cores) >> > >'the number of NVMe hardware queues' above should be the number of >single NVMe drive. >I believe 32 hw queues is common, also poll queues may take several from >the total 32. >When interrupt handling on single CPU core can't catch up with NVMe's IO >handling, soft lockup could be triggered. Of course, there are lot kinds of >supported processors by Linux. > >Also when (nr_nvme_drives * nr_nvme_hw_queues) > nr_cpu_cores, one >same CPU can be assigned to handle more than 1 nvme IO queue interrupt >from different NVMe drive, the situation becomes worse. > > >Thanks, >Ming _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme
next prev parent reply index Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-11-08 3:55 [PATCH 0/2] nvme-pci: improve IO performance via poll after batch submission Ming Lei 2019-11-08 3:55 ` [PATCH 1/2] nvme-pci: move sq/cq_poll lock initialization into nvme_init_queue Ming Lei 2019-11-08 4:12 ` Keith Busch 2019-11-08 7:09 ` Ming Lei 2019-11-08 3:55 ` [PATCH 2/2] nvme-pci: poll IO after batch submission for multi-mapping queue Ming Lei 2019-11-11 20:44 ` Christoph Hellwig 2019-11-12 0:33 ` Long Li 2019-11-12 1:35 ` Sagi Grimberg 2019-11-12 2:39 ` Ming Lei 2019-11-12 16:25 ` Hannes Reinecke 2019-11-12 16:49 ` Keith Busch 2019-11-12 17:29 ` Hannes Reinecke 2019-11-13 3:05 ` Ming Lei 2019-11-13 3:17 ` Keith Busch 2019-11-13 3:57 ` Ming Lei 2019-11-12 21:20 ` Long Li [this message] 2019-11-12 21:36 ` Keith Busch 2019-11-13 0:50 ` Long Li 2019-11-13 2:24 ` Ming Lei 2019-11-12 2:07 ` Ming Lei 2019-11-12 1:44 ` Sagi Grimberg 2019-11-12 9:56 ` Ming Lei 2019-11-12 17:35 ` Sagi Grimberg 2019-11-12 21:17 ` Long Li 2019-11-12 23:44 ` Jens Axboe 2019-11-13 2:47 ` Ming Lei 2019-11-12 18:11 ` Nadolski, Edmund 2019-11-13 13:46 ` Ming Lei
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