> "Michael S. Tsirkin" <mst@xxxxxxxxxx> 02/02/2011 03:11 AM
>
> On Tue, Feb 01, 2011 at 01:28:45PM -0800, Shirley Ma wrote:
> > On Tue, 2011-02-01 at 23:21 +0200, Michael S. Tsirkin wrote:
> > > Confused. We compare capacity to skb frags, no?
> > > That's sg I think ...
> >
> > Current guest kernel use indirect buffers, num_free returns how many
> > available descriptors not skb frags. So it's wrong here.
> >
> > Shirley
>
> I see. Good point. In other words when we complete the buffer
> it was indirect, but when we add a new one we
> can not allocate indirect so we consume.
> And then we start the queue and add will fail.
> I guess we need some kind of API to figure out
> whether the buf we complete was indirect?
>
> Another failure mode is when skb_xmit_done
> wakes the queue: it might be too early, there
> might not be space for the next packet in the vq yet.
I am not sure if this is the problem - shouldn't you
see these messages:
if (likely(capacity == -ENOMEM)) {
dev_warn(&dev->dev,
"TX queue failure: out of memory\n");
} else {
dev->stats.tx_fifo_errors++;
dev_warn(&dev->dev,
"Unexpected TX queue failure: %d\n",
capacity);
}
in next xmit? I am not getting this in my testing.
> A solution might be to keep some kind of pool
> around for indirect, we wanted to do it for block anyway ...
Your vhost patch should fix this automatically. Right?
Thanks,
- KK
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