Re: [dpdk-dev] [PATCH v4] vhost: Add indirect descriptors support to the TX path

["Wang, Zhihong" <zhihong.wang@intel.com>]

> -----Original Message-----
> From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
> Sent: Thursday, October 27, 2016 5:55 PM
> To: Wang, Zhihong <zhihong.wang@intel.com>; Yuanhan Liu
> <yuanhan.liu@linux.intel.com>; stephen@networkplumber.org; Pierre
> Pfister (ppfister) <ppfister@cisco.com>
> Cc: Xie, Huawei <huawei.xie@intel.com>; dev@dpdk.org;
> vkaplans@redhat.com; mst@redhat.com
> Subject: Re: [dpdk-dev] [PATCH v4] vhost: Add indirect descriptors support
> to the TX path
> 
> 
> 
> On 10/27/2016 11:10 AM, 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.
> > 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.
> As a first test, I tried again Txonly from the guest to the host (Rxonly),
> where Tx indirect descriptors are used, on my E5-2665 @2.40GHz:
> v16.11-rc1: 10.81Mpps
> v16.11-rc2: 10.91Mpps
> 
> -rc2 is even slightly better in my case.
> Could you please run the same test on your platform?

I mean to use rc2 as both host and guest, and compare the
perf between indirect=0 and indirect=1.

I use PVP traffic, tried both testpmd and OvS as the forwarding
engine in host, and testpmd in guest.

Thanks
Zhihong

> 
> And could you provide me more info on your fwd bench?
> Do you use dpdk-pktgen on host, or you do fwd on howt with a real NIC
> also?
> 
> Thanks,
> Maxime
> > Thanks,
> > Maxime
> >
> >>
> >>
> >> Thanks
> >> Zhihong
> >>
> >>> -----Original Message-----
> >>> From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
> >>> Sent: Monday, October 17, 2016 10:15 PM
> >>> To: Yuanhan Liu <yuanhan.liu@linux.intel.com>
> >>> Cc: Wang, Zhihong <zhihong.wang@intel.com>; Xie, Huawei
> >>> <huawei.xie@intel.com>; dev@dpdk.org; vkaplans@redhat.com;
> >>> mst@redhat.com; stephen@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