On Sun, 2011-12-11 at 14:25 +0200, Michael S. Tsirkin wrote: > Forwarding some results by Amos, who run multiple netperf streams in > parallel, from an external box to the guest. TCP_STREAM results were > noisy. This could be due to buffering done by TCP, where packet size > varies even as message size is constant. > > TCP_RR results were consistent. In this benchmark, after switching > to mandatory barriers, CPU utilization increased by up to 35% while > throughput went down by up to 14%. the normalized throughput/cpu > regressed consistently, between 7 and 35% > > The "fix" applied was simply this: What machine & processor was this ? Cheers, Ben. > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index 3198f2e..fdccb77 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -23,7 +23,7 @@ > > /* virtio guest is communicating with a virtual "device" that actually runs on > * a host processor. Memory barriers are used to control SMP effects. */ > -#ifdef CONFIG_SMP > +#if 0 > /* Where possible, use SMP barriers which are more lightweight than mandatory > * barriers, because mandatory barriers control MMIO effects on accesses > * through relaxed memory I/O windows (which virtio does not use). */ > > > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
