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'm using RC2, and the CPU is Xeon E5-2699 v3 @ 2.30GHz. Could you please verify if this is true in your test? 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
