From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yuanhan Liu Subject: Re: [PATCH 0/6] vhost: add Tx zero copy support Date: Tue, 23 Aug 2016 22:53:22 +0800 Message-ID: <20160823145322.GR30752@yliu-dev.sh.intel.com> References: <1471939839-29778-1-git-send-email-yuanhan.liu@linux.intel.com> <7eeb0acd-e98d-1dcd-793f-0b5f4b74874c@redhat.com> <20160823144211.GP30752@yliu-dev.sh.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: dev@dpdk.org To: Maxime Coquelin Return-path: Received: from mga06.intel.com (mga06.intel.com [134.134.136.31]) by dpdk.org (Postfix) with ESMTP id B2A293990 for ; Tue, 23 Aug 2016 16:43:36 +0200 (CEST) Content-Disposition: inline In-Reply-To: <20160823144211.GP30752@yliu-dev.sh.intel.com> List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" BTW, I really appreicate your efforts on reviewing this patchset. It would be great if you could take some time to review my another patchset :) [PATCH 0/7] vhost: vhost-cuse removal and code path refactoring It touchs a large of code base, that I wish I could apply it ASAP. So that the chance a later patch will introduce conflicts is small. --yliu On Tue, Aug 23, 2016 at 10:42:11PM +0800, Yuanhan Liu wrote: > On Tue, Aug 23, 2016 at 04:18:40PM +0200, Maxime Coquelin wrote: > > > > > > On 08/23/2016 10:10 AM, Yuanhan Liu wrote: > > >This patch set enables vhost Tx zero copy. The majority work goes to > > >patch 4: vhost: add Tx zero copy. > > > > > >The basic idea of Tx zero copy is, instead of copying data from the > > >desc buf, here we let the mbuf reference the desc buf addr directly. > > > > > >The major issue behind that is how and when to update the used ring. > > >You could check the commit log of patch 4 for more details. > > > > > >Patch 5 introduces a new flag, RTE_VHOST_USER_TX_ZERO_COPY, to enable > > >Tx zero copy, which is disabled by default. > > > > > >Few more TODOs are left, including handling a desc buf that is across > > >two physical pages, updating release note, etc. Those will be fixed > > >in later version. For now, here is a simple one that hopefully it > > >shows the idea clearly. > > > > > >I did some quick tests, the performance gain is quite impressive. > > > > > >For a simple dequeue workload (running rxonly in vhost-pmd and runnin > > >txonly in guest testpmd), it yields 40+% performance boost for packet > > >size 1400B. > > > > > >For VM2VM iperf test case, it's even better: about 70% boost. > > > > This is indeed impressive. > > Somewhere else, you mention that there is a small regression with small > > packets. Do you have some figures to share? > > It could be 15% drop for PVP case with 64B packet size. The test topo is: > > nic 0 --> VM Rx --> VM Tx --> nic 0 > > Put simply, I run vhost-switch example in the host and run testpmd in > the guest. > > Though the number looks big, I don't think it's an issue. First of all, > it's disabled by default. Secondly, if you want to enable it, you should > be certain that the packet size is normally big, otherwise, you should > not bother to try with zero copy. > > > Also, with this feature OFF, do you see some regressions for both small > > and bigger packets? > > Good question. I didn't check it on purpose, but I did try when it's > disabled, the number I got is pretty the same as the one I got without > this feature. So, I would say I don't see regressions. Anyway, I could > do more tests to make sure. > > --yliu