From: Yuanhan Liu <yuanhan.liu@linux.intel.com>
To: Maxime Coquelin <maxime.coquelin@redhat.com>
Cc: souvikdey33 <sodey@sonusnet.com>,
stephen@networkplumber.org, huawei.xie@intel.com, dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH v2] add mtu set in virtio
Date: Thu, 8 Sep 2016 15:30:29 +0800 [thread overview]
Message-ID: <20160908073029.GM23158@yliu-dev.sh.intel.com> (raw)
In-Reply-To: <d141aa3a-e024-19ac-fe99-a9ea07002ce4@redhat.com>
On Wed, Sep 07, 2016 at 11:16:47AM +0200, Maxime Coquelin wrote:
>
>
> On 09/07/2016 05:25 AM, Yuanhan Liu wrote:
> >On Tue, Aug 30, 2016 at 09:57:39AM +0200, Maxime Coquelin wrote:
> >>Hi Souvik,
> >>
> >>On 08/30/2016 01:02 AM, souvikdey33 wrote:
> >>>Signed-off-by: Souvik Dey <sodey@sonusnet.com>
> >>>
> >>>Fixes: 1fb8e8896ca8 ("Signed-off-by: Souvik Dey <sodey@sonusnet.com>")
> >>>Reviewed-by: Stephen Hemminger <stephen@networkplumber.org>
> >>>
> >>>Virtio interfaces should also support setting of mtu, as in case of cloud
> >>>it is expected to have the consistent mtu across the infrastructure that
> >>>the dhcp server sends and not hardcoded to 1500(default).
> >>>---
> >>>drivers/net/virtio/virtio_ethdev.c | 12 ++++++++++++
> >>>1 file changed, 12 insertions(+)
> >>
> >>FYI, there are some on-going changes in the VIRTIO specification
> >>so that the VHOST interface exposes its MTU to its VIRTIO peer.
> >>It may also be used as an alternative of what you patch achieves.
> >>
> >>I am working on its implementation in Qemu/DPDK, our goal being to
> >>reduce performance drops for small packets with Rx mergeable buffers
> >>feature enabled.
> >
> >Mind to educate me a bit on how that works?
>
> Of course.
>
> Basically, this is a way to advise the MTU we want in the guest.
> In the guest, if GRO is not enabled:
> - In case of Kernel virtio-net, it could be used to
> size the SKBs at the expected MTU. If possible, we could disable Rx
> mergeable buffers.
> - In case of virtio PMD, if the MTU advised by host is lower than the
> pre-allocated mbuf size for the receive queue, then we should not need
> mergeable buffers.
Thanks for the explanation!
I see. So, the point is to avoid using mergeable buffers while it is
enabled.
> Does that sound reasonnable?
Yeah, maybe. Just don't know how well it may work in real life. Have
you got any rought data so far?
--yliu
> Do I miss something?
>
> Thanks,
> Maxime
next prev parent reply other threads:[~2016-09-08 7:30 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-29 23:02 souvikdey33
2016-08-30 7:57 ` Maxime Coquelin
2016-09-01 22:20 ` Dey, Souvik
2016-09-02 7:05 ` Maxime Coquelin
2016-09-07 2:11 ` Dey, Souvik
2016-09-07 8:28 ` Maxime Coquelin
2016-09-07 3:25 ` Yuanhan Liu
2016-09-07 9:16 ` Maxime Coquelin
2016-09-08 7:30 ` Yuanhan Liu [this message]
2016-09-08 7:50 ` Maxime Coquelin
2016-09-08 7:57 ` Yuanhan Liu
2016-09-09 3:44 ` Dey, Souvik
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