Re: [Qemu-devel] [PATCH v2] net: Flush queued packets when guest resumes

[Fam Zheng <famz@redhat.com>]

On Tue, 07/14 15:42, Michael S. Tsirkin wrote:
> On Tue, Jul 14, 2015 at 01:20:03PM +0100, Stefan Hajnoczi wrote:
> > On Fri, Jul 10, 2015 at 05:03:22PM +0800, Fam Zheng wrote:
> > > On Tue, 07/07 12:19, Michael S. Tsirkin wrote:
> > > > On Tue, Jul 07, 2015 at 05:09:09PM +0800, Fam Zheng wrote:
> > > > > On Tue, 07/07 11:13, Michael S. Tsirkin wrote:
> > > > > > On Tue, Jul 07, 2015 at 09:21:07AM +0800, Fam Zheng wrote:
> > > > > > > Since commit 6e99c63 "net/socket: Drop net_socket_can_send" and friends,
> > > > > > > net queues need to be explicitly flushed after qemu_can_send_packet()
> > > > > > > returns false, because the netdev side will disable the polling of fd.
> > > > > > > 
> > > > > > > This fixes the case of "cont" after "stop" (or migration).
> > > > > > > 
> > > > > > > Signed-off-by: Fam Zheng <famz@redhat.com>
> > > > > > 
> > > > > > Note virtio has its own handler which must be used to
> > > > > > flush packets - this one might run too early or too late.
> > > > > 
> > > > > Which handler do you mean? I don't think virtio-net handles resume now. (If it
> > > > > does, we probably should drop it together with this change, since it's needed
> > > > > by as all NICs.)
> > > > > 
> > > > > Fam
> > > > 
> > > > virtio_vmstate_change
> > > > 
> > > > It's all far from trivial. I suspect these whack-a-mole approach
> > > > spreading purge here and there will only create more bugs.
> > > > 
> > > > Why would we ever need to process network packets when
> > > > VM is not running? I don't see any point to it.
> > > > How about we simply stop the job processing network on
> > > > vm stop and restart on vm start?
> > > 
> > > I suppose it is too much for 2.4. I think this approach, adding
> > > qemu_flush_queued_packets(), is consistent with its existing usage (when a
> > > device is becoming active from inactive), like in e1000_write_config.
> > > 
> > > How about applying this and let's work on "stopping tap when VM not running"
> > > for 2.5?
> > 
> > Jason has gone happy on this and the virtio-net .can_receive() patch.
> > 
> > Michael: Any further comments?  Are you okay with this patch too?

FWIW, I am sending another virtio-net patch to flush at .set_status.

> 
> I think it doesn't help virtio - am I wrong?
> 

Right, virtio doesn't need this because it gets notified with '.set_status()'.
But this patch does help:

http://lists.nongnu.org/archive/html/qemu-devel/2015-07/msg01396.html

(as well as all other NICs).

Fam