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:

quoted

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

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