From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754928AbYEYUrf (ORCPT ); Sun, 25 May 2008 16:47:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751074AbYEYUr1 (ORCPT ); Sun, 25 May 2008 16:47:27 -0400 Received: from srv5.dvmed.net ([207.36.208.214]:49399 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750760AbYEYUr1 (ORCPT ); Sun, 25 May 2008 16:47:27 -0400 Message-ID: <4839D05C.4040309@garzik.org> Date: Sun, 25 May 2008 16:47:24 -0400 From: Jeff Garzik User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: Francis Moreau CC: linux-kernel@vger.kernel.org, jens.axboe@oracle.com Subject: Re: question about splice performance References: <38b2ab8a0805250812l2ecd424bh74a1694ed56460de@mail.gmail.com> In-Reply-To: <38b2ab8a0805250812l2ecd424bh74a1694ed56460de@mail.gmail.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Score: -4.4 (----) X-Spam-Report: SpamAssassin version 3.2.4 on srv5.dvmed.net summary: Content analysis details: (-4.4 points, 5.0 required) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Francis Moreau wrote: > Hi, > > I did a really basic benchmark and was suprise about the results. > > $ echo 3 > /proc/sys/vm/drop_caches > $ time splice-cp vmlinux /tmp/vmlinux > > real 0m10.158s > user 0m0.002s > sys 0m0.401s > > $ echo 3 > /proc/sys/vm/drop_caches > $ time cp vmlinux /tmp/vmlinux > > real 0m10.590s > user 0m0.017s > sys 0m0.459s > > > I was expecting splice-cp case to be faster. > > Could someone enlight me ? If you drop caches you are not measuring splice speed. Use ramfs for your tests (guarantees data is in cache) instead. Jeff