netdev - Re: [PATCH net-next 2/3] vhost_net: support in order feature

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Message-ID: <1c50dc69-49d5-0d19-dea9-4c97a2d99b5f@redhat.com>
Date:   Mon, 26 Nov 2018 11:52:07 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 2/3] vhost_net: support in order feature


On 2018/11/23 下午11:49, Michael S. Tsirkin wrote:
> On Fri, Nov 23, 2018 at 11:00:15AM +0800, Jason Wang wrote:
>> This makes vhost_net to support in order feature. This is as simple as
>> use datacopy path when it was negotiated. An alternative is not to
>> advertise in order when zerocopy is enabled which tends to be
>> suboptimal consider zerocopy may suffer from e.g HOL issues.
> Well IIRC vhost_zerocopy_signal_used is used to
> actually reorder used ring to match available ring.
> So with a big comment explaining why it is so,
> we could just enable IN_ORDER there too.
>

The problem is we allow switching between zerocopy and datacopy.

And what's more important, if we allow in order for zerocopy, a single 
packet delay may hang all the rest.

Thanks