RE: [RFC PATCH 2/2] macvtap: TX zero copy between guest and host kernel

Shirley Ma
2010-09-15T02:41:00Z

On Wed, 2010-09-15 at 09:50 +0800, Xin, Xiaohui wrote:
> I think what David said is what we have thought before in mp device.
> Since we are not sure the exact time the tx buffer was wrote though
> DMA operation.
> But the deadline is when the tx buffer was freed. So we only notify
> the vhost stuff
> about the write when tx buffer freed. But the deadline is maybe too
> late for performance.

Have you tried it? If so what's the performance penalty you have seen by
notifying vhost when tx buffer freed?

I am thinking to have a callback in skb destructor,
vhost_add_used_and_signal gets updated when skb is actually freed, vhost
vq & head need to be passed to the callback. This might requires vhost
ring size is at least as big as the lower device driver.

Thanks
Shirley