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 40A4ECCF9EB for ; Mon, 27 Oct 2025 16:09:28 +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=s0NAMJbgz2XKMJ3TsTW+O6FmmH6wsyo2o1sqgeqL8wU=; b=JK0faKj/wKUSNoY64/bT7PBHo2 YJBdNRkIgN+16VChBp5sYJrJIOgujqyrDaHTRahD0ox/s3rbr7OAnC3QPQgMpOzu+fkAHFBfoCfGq 8qe07iUrIHxWP5LpDyA2EoWlrcVg/gcQZZxiGHqUUHFlFKUqMKZ1ALyYdCKkc5TErqKshgsgxCly7 EmXj0VcR7Cg9/Q2Twz+9LMgynbNsBK4cyYFukXgaPFUkqFuNRJU7a/QQc7s42H12wRqsy/dnfmoOJ NWO6vrgh5Gpo+tAk5LfbsujcBZK38GcSnUr/FECNswiLCqHfsR8GBQPypUcLmcOueM0TeM5cAyW7g aBhApYBg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vDPme-0000000EHfa-2tma; Mon, 27 Oct 2025 16:09:24 +0000 Received: from tor.source.kernel.org ([172.105.4.254]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vDPmd-0000000EHfP-43gj for linux-nvme@lists.infradead.org; Mon, 27 Oct 2025 16:09:24 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 19236603C3; Mon, 27 Oct 2025 16:09:23 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 84C38C4CEFD; Mon, 27 Oct 2025 16:09:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1761581362; bh=PwGL0FdkTDfKpb61RrIyKJxfpVGR24FtiSgYofPOYq0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=EGss5I344KqTA87L5w+GqCL1Uri3FFGcrv2uYA03ZcFqRIZW4enecD9ba1Uxx7lvU d/efqgZZ6RP72E27AbJ/y8nAUXIxTeO8bHoHb1ABOS2KmB/TZLWMUxO6gq+bPJJYL+ ZRFAiq+0r302prnMS9koroWOWKGLHD+k60VhfLaJTEt+njvt1uCXZReiycZACVTt3p DN+t/A8R1XMXYNg2x0eDC4V7udFxNQgDKU2e417rbavg0VcZX0gYzSowcF1P67CxwO 60TBoX68dr2BR+hhTRYiXhZu0kXtschfqn2+ID8tutokw0TJtE2OHvOhGTnrio39Yz SA44bmoUuCnAw== Date: Mon, 27 Oct 2025 10:09:20 -0600 From: Keith Busch To: Christoph Hellwig Cc: Leon Romanovsky , Keith Busch , linux-nvme@lists.infradead.org Subject: Re: [PATCH] nvme-pci: always use blk_map_iter for metadata Message-ID: References: <20251020182444.2587155-1-kbusch@meta.com> <20251021071935.GA31479@lst.de> <20251026072551.GB12554@unreal> <20251027071353.GA13854@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251027071353.GA13854@lst.de> 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 Mon, Oct 27, 2025 at 08:13:53AM +0100, Christoph Hellwig wrote: > On Sun, Oct 26, 2025 at 09:25:51AM +0200, Leon Romanovsky wrote: > > > Maybe the data path should only use blk_dma_iter too. Is dma_map_bvec > > > that much faster for the single vector case? I'm going to test both on > > > real hardware and see if there's a difference in CPU utilization or > > > latency. > > > > We tried that path (remove special case for single segment), but for > > very performance oriented case: direct mode without IOMMU, no p2p and > > extremely powerful RAID (~94M IOPS), Jens and Kanchan saw performance > > drop. On consumer grade HW (~2M IOPS), the performance change was not > > noticed. > > Yes. Sorry, I wanted to reply something like this to Keith earlier but > managed to drop the ball. Yeah, no problem. I was reaching the same conclusion anyway and moved on.