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From: Long Li <longli@microsoft.com>
To: Keith Busch <kbusch@kernel.org>
Cc: Jens Axboe <axboe@fb.com>, Sagi Grimberg <sagi@grimberg.me>,
	Christoph Hellwig <hch@lst.de>,
	"linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>,
	Ming Lei <ming.lei@redhat.com>
Subject: RE: [PATCH 2/2] nvme-pci: poll IO after batch submission for multi-mapping queue
Date: Wed, 13 Nov 2019 00:50:26 +0000
Message-ID: <CY4PR21MB07411D73ACA4BA55BD608CB5CE760@CY4PR21MB0741.namprd21.prod.outlook.com> (raw)
In-Reply-To: <20191112213646.GA1964@redsun51.ssa.fujisawa.hgst.com>

>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 <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.
>
>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.

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  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
2019-11-12 21:36           ` Keith Busch
2019-11-13  0:50             ` Long Li [this message]
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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