From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 87319C4332F for ; Fri, 30 Sep 2022 15:16:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=7ug3iu3bEXF78gnrgDTdjFOkTTSr8wz2XMT9Oa9w0AI=; b=eYJWTrFWUsyOOvEoyPXJYtE/wM Z99tGCl9WY29keWr/OydyxWg3TIMKVn1L7SxOSDLbi0BwSV8pJaoCywLBA9dktGQc5YCU9SestoqS mN9NNHOBcvCA50AAs0QKrril4P35SvvbcgeQlq2EJI89YxpS/WwGJ4PdEYzVM3abigKzqlmRIG1VJ PDjri+ezy91vSlWBmyN/uzGkFAX64MnVIE9ELEG9FsliHfxuafV4CguDXTTorBXbsKQIPBKk5NJLU kuoka+tblFILYED4OZ87s11t8FimHwaH7V1fzvYjDjc0Qxt/g3vo2XRcO5AtOthmN3RwfNprhds1T 28SkUUOw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1oeHkm-00A6mb-4w; Fri, 30 Sep 2022 15:16:40 +0000 Received: from sin.source.kernel.org ([2604:1380:40e1:4800::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1oeHkQ-00A6Yr-Ad for linux-nvme@lists.infradead.org; Fri, 30 Sep 2022 15:16:19 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id 724EECE25F7; Fri, 30 Sep 2022 15:16:14 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EAD10C433D6; Fri, 30 Sep 2022 15:16:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1664550972; bh=ivbMMPx0EIBUlLwHU3p53chkbIAEt6dlqzQqe+SbtnU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=c6E++ATP+ikY3/hEwW7knO0JNWDL39kWA84nMeRTFeyIWYIuJ1WHgMs+zECY/v3nc CtQ4lFModWKWf7u5ddwgbqTLwV8wlybjyyIBTc4MljG8riW79tlhMYt6SqMVHiqjuO cOXih0t2YsMTUTkPLivfkyNjFzWKeIrF1X9vXSnLOOwkGV82azg+rC+TYalh4uOFGZ N4JrInxUuzOOEqtfSiJZA1K7pPejZ0lU0gsmpSxoxpH7RCuOChFV/oW+TwxPSaKgpk lqjdOjOmpwVqP5Od89E7wR38g0ET9HAgbC/PumcwyIin5/vTpqtQ13yyP+ivXsSgOf S3KIQR6uvuu2w== Date: Fri, 30 Sep 2022 09:16:07 -0600 From: Keith Busch To: Sagi Grimberg Cc: Max Gurtovoy , linux-nvme@lists.infradead.org, Christoph Hellwig , Chaitanya Kulkarni , linux-block@vger.kernel.org, Jens Axboe , Hannes Reinecke Subject: Re: [PATCH rfc] nvme: support io stats on the mpath device Message-ID: References: <20220928195510.165062-1-sagi@grimberg.me> <20220928195510.165062-2-sagi@grimberg.me> <760a7129-945c-35fa-6bd6-aa315d717bc5@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220930_081618_557822_858FDFA2 X-CRM114-Status: GOOD ( 18.63 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Thu, Sep 29, 2022 at 07:32:39PM +0300, Sagi Grimberg wrote: > > > > > 3. Do you have some performance numbers (we're touching the fast path > > > > here) ? > > > > > > This is pretty light-weight, accounting is per-cpu and only wrapped by > > > preemption disable. This is a very small price to pay for what we gain. > > > > It does add up, though, and some environments disable stats to skip the > > overhead. At a minimum, you need to add a check for blk_queue_io_stat() before > > assuming you need to account for stats. > > But QUEUE_FLAG_IO_STAT is set by nvme-mpath itself? > You mean disable IO stats in runtime? Yes, the user can disable it at any time. That actually makes things a bit tricky since it can be enabled at the start of an IO and disabled by the time it completes.