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 7FFAECCF9EB for ; Mon, 27 Oct 2025 07:14:03 +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=G0s9MwwxLq3gV7C6+9tWhyToaMARnCwXTEYBx/0Ceag=; b=16chEiqS1FxVZTHhIYPAWXTU+W D1UXlGbX1wHTvhEp9M1gmQ3DMPAs2SAkRGqIuRXAN1I1rGx4RdJK7kAmP04Xg9iJAd7IXaIHfK+oM YRvsWe/k01cpxm2ELpj6pbZQ+Db0RUNET5nAi4tEpgYFoE2yuFyv/0J4XIs0mQ5sVi51J6CmUUXYm 0+gI1yT3zmLUUgDGWETDJpNsEYh4t2cPAl7puImAgEGmL5WFZKIqhsrZFnZIjVtpX3a2JkUpTp9nr xugp0+GY4b4pmqI5/Y4h5BSmfyTwWIrVGkOTjhj7RoVoHCHdszRVbIoooR8NSg3HINijVZMDJEsqo nzYILKYA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vDHQW-0000000DGEH-2WSC; Mon, 27 Oct 2025 07:14:00 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vDHQU-0000000DGDR-1EG3 for linux-nvme@lists.infradead.org; Mon, 27 Oct 2025 07:13:59 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id CCA3F227A87; Mon, 27 Oct 2025 08:13:53 +0100 (CET) Date: Mon, 27 Oct 2025 08:13:53 +0100 From: Christoph Hellwig To: Leon Romanovsky Cc: Keith Busch , Christoph Hellwig , Keith Busch , linux-nvme@lists.infradead.org Subject: Re: [PATCH] nvme-pci: always use blk_map_iter for metadata Message-ID: <20251027071353.GA13854@lst.de> References: <20251020182444.2587155-1-kbusch@meta.com> <20251021071935.GA31479@lst.de> <20251026072551.GB12554@unreal> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251026072551.GB12554@unreal> User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251027_001358_479283_275FB074 X-CRM114-Status: GOOD ( 17.12 ) 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 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.