Messages in this thread | | | From | Juan Quintela <> | Subject | Re: [PATCHv2] virtio: put last seen used index into ring itself | Date | Tue, 18 May 2010 13:26:36 +0200 |
| |
"Michael S. Tsirkin" <mst@redhat.com> wrote: > Generally, the Host end of the virtio ring doesn't need to see where > Guest is up to in consuming the ring. However, to completely understand > what's going on from the outside, this information must be exposed. > For example, host can reduce the number of interrupts by detecting > that the guest is currently handling previous buffers. > > Fortunately, we have room to expand: the ring is always a whole number > of pages and there's hundreds of bytes of padding after the avail ring > and the used ring, whatever the number of descriptors (which must be a > power of 2). > > We add a feature bit so the guest can tell the host that it's writing > out the current value there, if it wants to use that. > > This is based on a patch by Rusty Russell, with the main difference > being that we dedicate a feature bit to guest to tell the host it is > writing the used index. This way we don't need to force host to publish > the last available index until we have a use for it. > > Another difference is that while the feature helps virtio-net, > there have been conflicting reports wrt virtio-blk. > The reason is unknown, it could be due to the fact that > virtio-blk does not bother to disable interrupts at all. > So for now, this patch only acks this feature for -net. > > Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
It looks good.
Later, Juan.
| |