[dpdk-dev] [PATCH 0/6] vhost: add Tx zero copy support

Maxime Coquelin maxime.coquelin at redhat.com
Tue Aug 23 16:18:40 CEST 2016



On 08/23/2016 10:10 AM, Yuanhan Liu wrote:
> This patch set enables vhost Tx zero copy. The majority work goes to
> patch 4: vhost: add Tx zero copy.
>
> The basic idea of Tx zero copy is, instead of copying data from the
> desc buf, here we let the mbuf reference the desc buf addr directly.
>
> The major issue behind that is how and when to update the used ring.
> You could check the commit log of patch 4 for more details.
>
> Patch 5 introduces a new flag, RTE_VHOST_USER_TX_ZERO_COPY, to enable
> Tx zero copy, which is disabled by default.
>
> Few more TODOs are left, including handling a desc buf that is across
> two physical pages, updating release note, etc. Those will be fixed
> in later version. For now, here is a simple one that hopefully it
> shows the idea clearly.
>
> I did some quick tests, the performance gain is quite impressive.
>
> For a simple dequeue workload (running rxonly in vhost-pmd and runnin
> txonly in guest testpmd), it yields 40+% performance boost for packet
> size 1400B.
>
> For VM2VM iperf test case, it's even better: about 70% boost.

This is indeed impressive.
Somewhere else, you mention that there is a small regression with small
packets. Do you have some figures to share?

Also, with this feature OFF, do you see some regressions for both small
and bigger packets?

Thanks,
Maxime
>
> ---
> Yuanhan Liu (6):
>   vhost: simplify memory regions handling
>   vhost: get guest/host physical address mappings
>   vhost: introduce last avail idx for Tx
>   vhost: add Tx zero copy
>   vhost: add a flag to enable Tx zero copy
>   examples/vhost: add an option to enable Tx zero copy
>
>  doc/guides/prog_guide/vhost_lib.rst |   7 +-
>  examples/vhost/main.c               |  19 ++-
>  lib/librte_vhost/rte_virtio_net.h   |   1 +
>  lib/librte_vhost/socket.c           |   5 +
>  lib/librte_vhost/vhost.c            |  12 ++
>  lib/librte_vhost/vhost.h            | 103 +++++++++----
>  lib/librte_vhost/vhost_user.c       | 297 +++++++++++++++++++++++-------------
>  lib/librte_vhost/virtio_net.c       | 188 +++++++++++++++++++----
>  8 files changed, 472 insertions(+), 160 deletions(-)
>


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