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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1iUdqL-000796-Vs; Tue, 12 Nov 2019 21:36:57 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1iUdqI-00078g-Dd for linux-nvme@lists.infradead.org; Tue, 12 Nov 2019 21:36:55 +0000 Received: from redsun51.ssa.fujisawa.hgst.com (unknown [199.255.47.7]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8F99B20674; Tue, 12 Nov 2019 21:36:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573594613; bh=KT2GjEt3BEczXBeaCO4w7FFghD60f6gHZa3tcZVioL4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=nYuSmGGFUaa3cYvTQ9FUyYs149ix8UO8LpOWE0oEtD/E5wkiNIckGQ1EQR3nqg3lE 4/F/vhPtHcCwjXeTn+Mcn+7UUTNmmz/bRNNyf//HsKgm/LUnXylYs8Q4t5pBP48Fur DXVV4MYso9rOhEnJJlHJOJNdpuM+ajrX51ytvRm4= Date: Wed, 13 Nov 2019 06:36:46 +0900 From: Keith Busch To: Long Li Subject: Re: [PATCH 2/2] nvme-pci: poll IO after batch submission for multi-mapping queue Message-ID: <20191112213646.GA1964@redsun51.ssa.fujisawa.hgst.com> References: <20191108035508.26395-1-ming.lei@redhat.com> <20191108035508.26395-3-ming.lei@redhat.com> <20191111204446.GA26028@lst.de> <20191112023920.GD15079@ming.t460p> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191112_133654_481584_7516E924 X-CRM114-Status: GOOD ( 15.94 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jens Axboe , Sagi Grimberg , Christoph Hellwig , "linux-nvme@lists.infradead.org" , Ming Lei Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org 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? _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme