> -----Original Message----- > From: Yuanhan Liu [mailto:yuanhan.liu at linux.intel.com] > Sent: Thursday, October 27, 2016 6:46 PM > To: Maxime Coquelin <maxime.coquelin at redhat.com> > Cc: Wang, Zhihong <zhihong.wang at intel.com>; > stephen at networkplumber.org; Pierre Pfister (ppfister) > <ppfister at cisco.com>; Xie, Huawei <huawei.xie at intel.com>; dev at > dpdk.org; > vkaplans at redhat.com; mst at redhat.com > Subject: Re: [dpdk-dev] [PATCH v4] vhost: Add indirect descriptors support > to the TX path > > On Thu, Oct 27, 2016 at 12:35:11PM +0200, Maxime Coquelin wrote: > > > > > > On 10/27/2016 12:33 PM, Yuanhan Liu wrote: > > >On Thu, Oct 27, 2016 at 11:10:34AM +0200, Maxime Coquelin wrote: > > >>Hi Zhihong, > > >> > > >>On 10/27/2016 11:00 AM, Wang, Zhihong wrote: > > >>>Hi Maxime, > > >>> > > >>>Seems indirect desc feature is causing serious performance > > >>>degradation on Haswell platform, about 20% drop for both > > >>>mrg=on and mrg=off (--txqflags=0xf00, non-vector version), > > >>>both iofwd and macfwd. > > >>I tested PVP (with macswap on guest) and Txonly/Rxonly on an Ivy > Bridge > > >>platform, and didn't faced such a drop. > > > > > >I was actually wondering that may be the cause. I tested it with > > >my IvyBridge server as well, I saw no drop. > > > > > >Maybe you should find a similar platform (Haswell) and have a try? > > Yes, that's why I asked Zhihong whether he could test Txonly in guest to > > see if issue is reproducible like this. > > I have no Haswell box, otherwise I could do a quick test for you. IIRC, > he tried to disable the indirect_desc feature, then the performance > recovered. So, it's likely the indirect_desc is the culprit here. > > > I will be easier for me to find an Haswell machine if it has not to be > > connected back to back to and HW/SW packet generator.
In fact simple loopback test will also do, without pktgen. Start testpmd in both host and guest, and do "start" in one and "start tx_first 32" in another. Perf drop is about 24% in my test. > > Makes sense. > > --yliu > > > > Thanks, > > Maxime > > > > > > > > --yliu > > > > > >>Have you tried to pass indirect_desc=off to qemu cmdline to see if you > > >>recover the performance? > > >> > > >>Yuanhan, which platform did you use when you tested it with zero copy? > > >> > > >>> > > >>>I'm using RC2, and the CPU is Xeon E5-2699 v3 @ 2.30GHz. > > >>> > > >>>Could you please verify if this is true in your test? > > >>I'll try -rc1/-rc2 on my platform, and let you know. > > >> > > >>Thanks, > > >>Maxime > > >> > > >>> > > >>> > > >>>Thanks > > >>>Zhihong > > >>> > > >>>>-----Original Message----- > > >>>>From: Maxime Coquelin [mailto:maxime.coquelin at redhat.com] > > >>>>Sent: Monday, October 17, 2016 10:15 PM > > >>>>To: Yuanhan Liu <yuanhan.liu at linux.intel.com> > > >>>>Cc: Wang, Zhihong <zhihong.wang at intel.com>; Xie, Huawei > > >>>><huawei.xie at intel.com>; dev at dpdk.org; vkaplans at redhat.com; > > >>>>mst at redhat.com; stephen at networkplumber.org > > >>>>Subject: Re: [dpdk-dev] [PATCH v4] vhost: Add indirect descriptors > support > > >>>>to the TX path > > >>>> > > >>>> > > >>>> > > >>>>On 10/17/2016 03:21 PM, Yuanhan Liu wrote: > > >>>>>On Mon, Oct 17, 2016 at 01:23:23PM +0200, Maxime Coquelin wrote: > > >>>>>>>On my side, I just setup 2 Windows 2016 VMs, and confirm the > issue. > > >>>>>>>I'll continue the investigation early next week. > > >>>>>> > > >>>>>>The root cause is identified. > > >>>>>>When INDIRECT_DESC feature is negotiated, Windows guest uses > indirect > > >>>>>>for both Tx and Rx descriptors, whereas Linux guests (Virtio PMD & > > >>>>>>virtio-net kernel driver) use indirect only for Tx. > > >>>>>>I'll implement indirect support for the Rx path in vhost lib, but the > > >>>>>>change will be too big for -rc release. > > >>>>>>I propose in the mean time to disable INDIRECT_DESC feature in > vhost > > >>>>>>lib, we can still enable it locally for testing. > > >>>>>> > > >>>>>>Yuanhan, is it ok for you? > > >>>>> > > >>>>>That's okay. > > >>>>I'll send a patch to disable it then. > > >>>> > > >>>>> > > >>>>>> > > >>>>>>>Has anyone already tested Windows guest with vhost-net, which > also > > >>>>has > > >>>>>>>indirect descs support? > > >>>>>> > > >>>>>>I tested and confirm it works with vhost-net. > > >>>>> > > >>>>>I'm a bit confused then. IIRC, vhost-net also doesn't support indirect > > >>>>>for Rx path, right? > > >>>> > > >>>>No, it does support it actually. > > >>>>I thought it didn't support too, I misread the Kernel implementation of > > >>>>vhost-net and virtio-net. Acutally, virtio-net makes use of indirect > > >>>>in Rx path when mergeable buffers is disabled. > > >>>> > > >>>>The confusion certainly comes from me, sorry about that. > > >>>> > > >>>>Maxime
