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Thu, 13 Feb 2020 19:41:08 -0500 X-MC-Unique: f0p-8FSRMHGRhhX31onxaw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 32B1C8017CC; Fri, 14 Feb 2020 00:41:07 +0000 (UTC) Received: from ming.t460p (ovpn-8-16.pek2.redhat.com [10.72.8.16]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4997860BF4; Fri, 14 Feb 2020 00:41:00 +0000 (UTC) Date: Fri, 14 Feb 2020 08:40:56 +0800 From: Ming Lei To: Keith Busch Subject: Re: [LSF/MM/BPF TOPIC] NVMe HDD Message-ID: <20200214004056.GC4907@ming.t460p> References: <20200211122821.GA29811@ming.t460p> <20200212220328.GB25314@ming.t460p> <20200213075348.GA9144@ming.t460p> <20200213083413.GC9144@ming.t460p> <20200213163038.GB7634@redsun51.ssa.fujisawa.hgst.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200213163038.GB7634@redsun51.ssa.fujisawa.hgst.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200213_164114_629633_1AFD4629 X-CRM114-Status: GOOD ( 13.46 ) 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: "linux-block@vger.kernel.org" , Damien Le Moal , Tim Walker , "linux-nvme@lists.infradead.org" , linux-scsi 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 Fri, Feb 14, 2020 at 01:30:38AM +0900, Keith Busch wrote: > On Thu, Feb 13, 2020 at 04:34:13PM +0800, Ming Lei wrote: > > On Thu, Feb 13, 2020 at 08:24:36AM +0000, Damien Le Moal wrote: > > > Got it. And since queue full will mean no more tags, submission will block > > > on get_request() and there will be no chance in the elevator to merge > > > anything (aside from opportunistic merging in plugs), isn't it ? > > > So I guess NVMe HDDs will need some tuning in this area. > > > > scheduler queue depth is usually 2 times of hw queue depth, so requests > > ar usually enough for merging. > > > > For NVMe, there isn't ns queue depth, such as scsi's device queue depth, > > meantime the hw queue depth is big enough, so no chance to trigger merge. > > Most NVMe devices contain a single namespace anyway, so the shared tag > queue depth is effectively the ns queue depth, and an NVMe HDD should > advertise queue count and depth capabilities orders of magnitude lower > than what we're used to with nvme SSDs. That should get merging and > BLK_STS_DEV_RESOURCE handling to occur as desired, right? Right. The advertised queue depth might serve two purposes: 1) reflect the namespace's actual queueing capability, so block layer's merging is possible 2) avoid timeout caused by too many in-flight IO Thanks, Ming _______________________________________________ linux-nvme mailing list linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme