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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org >Subject: Re: [PATCH 2/2] nvme-pci: poll IO after batch submission for multi- >mapping queue > >On Tue, Nov 12, 2019 at 09:20:27PM +0000, Long Li wrote: >> >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 >> >> >Sent: Monday, November 11, 2019 12:45 PM >> >> >To: Ming Lei >> >> >Cc: linux-nvme@lists.infradead.org; Keith Busch >> >> >; Jens Axboe ; Christoph Hellwig >> >> >; Sagi Grimberg ; Long Li >> >> > >> >> >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. > >What if you just use threaded interrupts with the path that scheduels the >bottom-half on any CPU in the mask? Does that resolve lockup? Yes, that patch also fixed the soft lockup problem. But it also introduced a performance regression, the peak IOPS dropped 40%. The reason is that I/O issuing processes (FIO in the tests) get more involuntary schedules. _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme