On 08/23/2016 04:53 PM, Yuanhan Liu wrote: > 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.
Sure, I will try to review it by tomorrow morning (CET). REgards, Maxime > > --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
