From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Monjalon Subject: Re: [PATCH v8 1/3] eal/x86: run-time dispatch over memcpy Date: Thu, 02 Nov 2017 13:15:46 +0100 Message-ID: <10650787.QzmVRp3hPH@xps> References: <1507206794-79941-1-git-send-email-xiaoyun.li@intel.com> <2027509.fDzOy6Rher@xps> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Cc: "Wang, Zhihong" , dev@dpdk.org, "Richardson, Bruce" , "Ananyev, Konstantin" , "Lu, Wenzhuo" , "Zhang, Helin" , "ophirmu@mellanox.com" To: "Li, Xiaoyun" Return-path: Received: from out4-smtp.messagingengine.com (out4-smtp.messagingengine.com [66.111.4.28]) by dpdk.org (Postfix) with ESMTP id 348821B3C6 for ; Thu, 2 Nov 2017 13:15:47 +0100 (CET) In-Reply-To: List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" 02/11/2017 11:58, Li, Xiaoyun: > From: Thomas Monjalon [mailto:thomas@monjalon.net] > > 02/11/2017 11:22, Wang, Zhihong: > > > > I don't know what is creating this drop exactly. > > > > When doing different tests on different environments, we do not see > > > > this drop. > > > > If nobody else can see such issue, I guess we can ignore it. > > > > > > Hi Thomas, Xiaoyun, > > > > > > With this patch (commit 84cc318424d49372dd2a5fbf3cf84426bf95acce) I > > > see more than 20% performance drop in vhost loopback test with testpmd > > > macswap for 256 bytes packets, which means it impacts actual > > > vSwitching performance. > > > > > > Suggest we fix it or revert it for this release. > > > > I think we need more numbers to take a decision. > > What is the benefit of this patch? In which use-cases? > > The benefit is that if compile it on a lower platform (such as only supports SSE), > when it run on higher platforms (such as AVX2 or AVX512). It would still can get ISA benefit (AVX2). Yes, but you don't provide any number here. > User case seems to be that some customers want it in cloud environment and don't want to compile on all platforms. > > > What are the drawbacks? In which use-cases? > > The drawback is perf drop. So far, see lot of drop in mellanox case and vhost case. > > Should I send the revert patch or you revert it directly? You should send the revert yourself with some good justifications. I did not ask some numbers when accepting the patch (my mistake). Please provide the numbers for the revert. > > Please, it is a call to test performance with and without this patch in more > > environments (CPU, packet size, applications). Who can test it in more environments?