linux-kernel - Re: [PATCH RFC v8 02/11] vhost: use batched get_vq

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Message-ID: <CAJaqyWe1+FmPC9L_+8oGfYUT63BaWuGrOnkRnUcGapvwtzqmPw@mail.gmail.com>
Date:   Fri, 19 Jun 2020 20:25:48 +0200
From:   Eugenio Perez Martin <eperezma@...hat.com>
To:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        linux-kernel@...r.kernel.org, kvm list <kvm@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        Jason Wang <jasowang@...hat.com>
Subject: Re: [PATCH RFC v8 02/11] vhost: use batched get_vq_desc version

On Fri, Jun 19, 2020 at 8:07 PM Eugenio Perez Martin
<eperezma@...hat.com> wrote:
>
> On Mon, Jun 15, 2020 at 2:28 PM Eugenio Perez Martin
> <eperezma@...hat.com> wrote:
> >
> > On Thu, Jun 11, 2020 at 5:22 PM Konrad Rzeszutek Wilk
> > <konrad.wilk@...cle.com> wrote:
> > >
> > > On Thu, Jun 11, 2020 at 07:34:19AM -0400, Michael S. Tsirkin wrote:
> > > > As testing shows no performance change, switch to that now.
> > >
> > > What kind of testing? 100GiB? Low latency?
> > >
> >
> > Hi Konrad.
> >
> > I tested this version of the patch:
> > https://lkml.org/lkml/2019/10/13/42
> >
> > It was tested for throughput with DPDK's testpmd (as described in
> > http://doc.dpdk.org/guides/howto/virtio_user_as_exceptional_path.html)
> > and kernel pktgen. No latency tests were performed by me. Maybe it is
> > interesting to perform a latency test or just a different set of tests
> > over a recent version.
> >
> > Thanks!
>
> I have repeated the tests with v9, and results are a little bit different:
> * If I test opening it with testpmd, I see no change between versions
> * If I forward packets between two vhost-net interfaces in the guest
> using a linux bridge in the host:
>   - netperf UDP_STREAM shows a performance increase of 1.8, almost
> doubling performance. This gets lower as frame size increase.
>   - rests of the test goes noticeably worse: UDP_RR goes from ~6347
> transactions/sec to 5830
>   - TCP_STREAM goes from ~10.7 gbps to ~7Gbps
>   - TCP_RR from 6223.64 transactions/sec to 5739.44

And I forgot to add: It seems that avoiding IOV length math helps,
since performance increases in all tests from patch 02/11 ("vhost: use
batched get_vq_desc version") to 11/11 ("vhost: drop head based
APIs").