On 06/06/2016 15:55, Michael S. Tsirkin wrote: > > According to the spec, if the VIRTIO_RING_F_EVENT_IDX feature bit is > > negotiated the driver MUST set flags to 0. Not dirtying the available > > ring in virtqueue_disable_cb may also have a positive performance impact. > > Question would be, is this a gain or a loss. We have an extra branch, > and the write might serve to prefetch the cache line. > > > Writes to the used event field (vring_used_event) are still unconditional. > > > > Signed-off-by: Ladi Prosek <lprosek@xxxxxxxxxx> > > Wow you are right wrt the spec. Should we change the spec or the > code though? I would change the spec and note that bit 0 of the flags is ignored if event indices are in use. Paolo -- 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
