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. 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
