Messages in this thread | | | Subject | Re: [PATCH net] Revert "vhost: cache used event for better performance" | From | Jason Wang <> | Date | Wed, 26 Jul 2017 21:18:02 +0800 |
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On 2017年07月26日 20:57, Michael S. Tsirkin wrote: > On Wed, Jul 26, 2017 at 04:03:17PM +0800, Jason Wang wrote: >> This reverts commit 809ecb9bca6a9424ccd392d67e368160f8b76c92. Since it >> was reported to break vhost_net. We want to cache used event and use >> it to check for notification. We try to valid cached used event by >> checking whether or not it was ahead of new, but this is not correct >> all the time, it could be stale and there's no way to know about this. >> >> Signed-off-by: Jason Wang<jasowang@redhat.com> > Could you supply a bit more data here please? How does it get stale? > What does guest need to do to make it stale? This will be helpful if > anyone wants to bring it back, or if we want to extend the protocol. >
The problem we don't know whether or not guest has published a new used event. The check vring_need_event(vq->last_used_event, new + vq->num, new) is not sufficient to check for this.
Thanks
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