On Saturday 05 January 2008 09:24:40 Anthony Liguori wrote:
> Hey Rusty et al,
>
> I've got automatic backports of the virtio modules[1] working back to
> 2.6.18. Everything seems okay except that for any kernel with the older
> NAPI api, performance is extremely bad. I get about 1gbit on TX with
> 2.6.24 but I get somewhere around 20mbit on 2.6.22.
OK, I tested this backport and immediately got oopses. Revealed some
interesting races in net driver (again, it's that damn callback disable
causing problems). New queue fixes these, but get awful performance:
'dd bs=1M count=1000 if=/dev/zero | nc 172.20.0.1 8889' takes almost 30
seconds.
Found one bug in your code tho: if enable_cb returns false, it means the queue
has *not* been enabled:
--- hack-module.awk.~1~ 2008-01-06 10:49:16.000000000 +1100
+++ hack-module.awk 2008-01-07 19:08:40.000000000 +1100
@@ -49,7 +49,6 @@
print " netif_rx_complete(vi->dev);";
print "";
print " if (!no_work && netif_rx_reschedule(vi->dev, received)) {";
- print " vi->rvq->vq_ops->disable_cb(vi->rvq);";
print " skb = NULL;";
print " goto again;";
print " }";
Will continue looking for performance regression tomorrow (actually, better
check my changes haven't introduced it in non-backports first!).
Thanks!
Rusty.
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