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 66420CC6B38 for ; Fri, 16 Oct 2026 17:27:13 +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-Transfer-Encoding:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=KBEGJr9zQZy95V5Zr1A1ig2Oaq2yE9CW2KUEvun7wpA=; b=4lRSkb0vjjxHS2ie0VhU/e5olA hgFwfN4TqNNrTf6kB710B9b2HN6K7RiIfYoIHeTgjboO1IG5QbH3bAG3DjxN1zJi6PWbry4+401CL uGX1Ekcc5WYIJU34aXzvTeYz+e2AGbcRwkceaCiIHP0FLbM4cQnH5NblWdQYFgckz99Elve+zN0AD OoaeCrShS6yFf2WHxRLDYgo0hXYCmARY8TG1Ol9Lc1dj7TzZ+EMkcicPVRCg6KmonfV8xooaSRa4k DUUjle+2zkv3+GUvYNtPg/zrUEGKk8s3igpq/bonLlDovc6pAQH+lqR3vgvepyMdcAzffonYwzlcK qk0FdOjw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xHli3-00000003YXL-1JKC; Fri, 16 Oct 2026 17:27:11 +0000 Received: from sea.source.kernel.org ([172.234.252.31]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1xHli2-00000003YXF-0HIj for linux-nvme@lists.infradead.org; Fri, 16 Oct 2026 17:27:10 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 8C98E43715; Fri, 16 Oct 2026 17:27:09 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 315231F000C5; Fri, 16 Oct 2026 17:27:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792171629; bh=KBEGJr9zQZy95V5Zr1A1ig2Oaq2yE9CW2KUEvun7wpA=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=KnyCjP78vlFuxveebZ9MofPRrsYmdol4uKYwfMmoiuiHuM+wbJ8/YceLl6b6b4r1s XP59RMcjHLCO9sACz7vfhn0nAqdRgKm15yCQ1Oakt5D7Zy4w64V5ETAUN/JeNOe0uQ KNMZCR/vVn4+BSVbHFGy3EqlEb+YKal89csVJTirWnfnBDxB/c8cAqX4SUEGigostS ifGzr+0u/3HODTylWhsY4UmgLfx+TWMQr83gjwI5ihsnPNC/2oqlxtyMOos5yYHsnD wrduJ4vdPCS5itMFeKxZvM2xSykFoY4tkVSWMOlI1BIzYAreDsUzXN0WwmK21W8D9C i1Dok6Nf1el1g== Date: Fri, 16 Oct 2026 11:27:07 -0600 From: Keith Busch To: Erwan Velu Cc: linux-nvme@lists.infradead.org, axboe@kernel.dk, hch@lst.de, sagi@grimberg.me, linux-kernel@vger.kernel.org, Erwan Velu Subject: Re: [PATCH] nvme: honor the volatile write cache enable state Message-ID: References: <20261016141208.2641974-1-e.velu@criteo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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 Fri, Oct 16, 2026 at 07:15:20PM +0200, Erwan Velu wrote: > Le ven. 16 oct. 2026 à 18:57, Keith Busch a écrit : > > > > On Fri, Oct 16, 2026 at 04:12:08PM +0200, Erwan Velu wrote: > > > job | cache | IOPS | fsync avg | flushes | gain > > > ----------------------+---------+--------+-----------+---------+------ > > > psync buffered, QD1 | back | 3885 | 247.6us | 116552 | > > > | through | 48325 | 15.7us | 0 | x12.4 > > > ----------------------+---------+--------+-----------+---------+------ > > > io_uring direct, QD1 | back | 3886 | 238.2us | 116593 | > > > | through | 41924 | 5.7us | 0 | x10.8 > > > ----------------------+---------+--------+-----------+---------+------ > > > io_uring direct, QD32 | back | 5088 | 6173.5us | 117793 | > > > | through | 140196 | 107.0us | 0 | x27.6 > > > > > > From NVMe 1.4c (sections 5.21.1.6 and 6.8) up to the NVMe Base > > > Specification 2.4 (sections 5.2.30.1.4 and 7.2), a Flush command has no > > > effect if the volatile write cache is not enabled. > > > > Yeah, the NVMe Flush operation should be a no-op in the device, so the > > dramatic performance difference is a bit alarming. Surely the block > > stack's flush machinery is not the reason for the difference, right? > > > > If the device's flush handling is this bad when VWC is disabled, what > > happens when you have it enabled? Can you re-run the same test with that > > setting? > > > > I'm not necessarily against what you're proposing here, but your numbers > > are unexpected. > > Maybe my table here isn't probably clear enough. > The numbers shown in the "write back" mode were done with VWC enabled. But you said the table came from tests "with WCE cleared" in the VWC feature. ?