Re: [PATCH] virtio: use smp_XX barriers

2010-01-27 Thread Michael S. Tsirkin
On Wed, Jan 27, 2010 at 11:46:32AM +0200, Avi Kivity wrote: > On 01/27/2010 11:36 AM, Michael S. Tsirkin wrote: >> >> >>> smp_mb() is used for processor-vs-processor ordering, which can't happen >>> on UP systems, but for process-vs-device, we must use mb(). >>> >>> (this shows up if running a UP g

Re: [PATCH] virtio: use smp_XX barriers

2010-01-27 Thread Avi Kivity
On 01/27/2010 11:36 AM, Michael S. Tsirkin wrote: > > >> smp_mb() is used for processor-vs-processor ordering, which can't happen >> on UP systems, but for process-vs-device, we must use mb(). >> >> (this shows up if running a UP guest on an SMP host). >> > Currently, yes. But virtio is not a

Re: [PATCH] virtio: use smp_XX barriers

2010-01-27 Thread Michael S. Tsirkin
On Wed, Jan 27, 2010 at 11:28:32AM +0200, Avi Kivity wrote: > On 01/21/2010 07:10 PM, Michael S. Tsirkin wrote: >> Documentation/memory-barriers.txt says: >> Mandatory barriers should not be used to control SMP effects, since >> mandatory barriers unnecessarily impose overhead on UP systems. >> >>

Re: [PATCH] virtio: use smp_XX barriers

2010-01-27 Thread Avi Kivity
On 01/21/2010 07:10 PM, Michael S. Tsirkin wrote: > Documentation/memory-barriers.txt says: > Mandatory barriers should not be used to control SMP effects, since > mandatory barriers unnecessarily impose overhead on UP systems. > > This rule applies to virtio, so let's do it correctly. > > Thi

[PATCH] virtio: use smp_XX barriers

2010-01-21 Thread Michael S. Tsirkin
Documentation/memory-barriers.txt says: Mandatory barriers should not be used to control SMP effects, since mandatory barriers unnecessarily impose overhead on UP systems. This rule applies to virtio, so let's do it correctly. Signed-off-by: Michael S. Tsirkin --- drivers/virtio/virtio_ring.c |