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 620D6C433FE for ; Thu, 29 Sep 2022 15:03:40 +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=XmNlTpL1FezqqiLizXeLtS41/5lylIhlx4eScxBoMCk=; b=Fkfy8YtO5GsTB4mhj02LXzxffy W0pG77aZw80lztV5cMf2gQcLpX7nNM4DvjoPkYANPUKQ6pAIRaBNu+oESXRt9d+qKVJ7U0H/wjSn7 5Ukj3RHFyFdtCLVwputm21wwCSnud4kKVgQfk3Nwnn39mNi/SO6unc86/6JwRrdxr3aKscNlKJ4k+ 7YGi3vmXGuG3Q9yEHwe917z4rYDXFGbIHGIFPK++qgueu0UqqdVQrCAx/+/HV3EvGRp91iA5DJ457 2pNNF/aDr/+ug2m+hwd4rZyCZ2e1ulP3HT0DOkGfkZQbrkiOqDgqXZ9/50peVRBMAHOgtiCHKhu7V ljCwPBfg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1odv4c-003kG7-2X; Thu, 29 Sep 2022 15:03:38 +0000 Received: from dfw.source.kernel.org ([139.178.84.217]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1odv4V-003kBd-JW for linux-nvme@lists.infradead.org; Thu, 29 Sep 2022 15:03:33 +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 dfw.source.kernel.org (Postfix) with ESMTPS id 52C09608D5; Thu, 29 Sep 2022 15:03:28 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1ADC3C433B5; Thu, 29 Sep 2022 15:03:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1664463807; bh=oe5t3MO6suf++0Q4/eQSbeDMVNrpcAiy/4s2fqFhZP4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=JDoTBl9s+q259YmmTDewsSNixuD2NqzHD3dTnP6Dx8Px1CYTMGo3ow9rNQO4ouGAn S3skrM+wSmSeXU1WqFSQtrIK3NY9kTWbtHkEKmIg4aqDvoRkg2ivHtohtyq8W89QB0 ZTsfGawiHVgbEa8oyENgZn77nSs7MKRoQiav/kDhzLCABXYjZOhFrMsD7ZwrmxNvNB sVTl9+PmPyIR9ymw4RyOh4F5LCyh49P/fcf3wxtqcrdJWccqjDr0OLMKgMBIag9nQT RkSMybalq0bwu/zqfRQJuj42ZplnPo3ckakRNT9hm8tAO794PCQFH5p/CoafoqcH2x tiO3X54PUXFQg== Date: Thu, 29 Sep 2022 09:03:24 -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-20220929_080331_693970_AF1CCAEA X-CRM114-Status: GOOD ( 14.37 ) 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 12:59:46PM +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. Instead of duplicating the accounting, could you just have the stats file report the sum of its hidden devices?