On Tue, 26 Feb 2013 13:13:39 +0100 Christian Borntraeger <borntraeger@xxxxxxxxxx> wrote: > On 26/02/13 12:18, Michael S. Tsirkin wrote: > > virtio_ccw: pass a cookie value to kvm hypercall > > > > Lookups by channel/vq pair on host during virtio notifications might be > > expensive. Interpret hypercall return value as a cookie which host can > > use to do device lookups for the next notification more efficiently. > > > > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > > > > --- > > > > diff --git a/drivers/s390/kvm/virtio_ccw.c b/drivers/s390/kvm/virtio_ccw.c > > index 2029b6c..1054f3a 100644 > > --- a/drivers/s390/kvm/virtio_ccw.c > > +++ b/drivers/s390/kvm/virtio_ccw.c > > @@ -77,6 +77,7 @@ struct virtio_ccw_vq_info { > > void *queue; > > struct vq_info_block *info_block; > > struct list_head node; > > + long cookie; > > }; > > > > #define KVM_VIRTIO_CCW_RING_ALIGN 4096 > > @@ -145,15 +146,18 @@ static int ccw_io_helper(struct virtio_ccw_device *vcdev, > > } > > > > static inline long do_kvm_notify(struct subchannel_id schid, > > - unsigned long queue_index) > > + unsigned long queue_index, > > + long cookie) > > { > > register unsigned long __nr asm("1") = KVM_S390_VIRTIO_CCW_NOTIFY; > > register struct subchannel_id __schid asm("2") = schid; > > register unsigned long __index asm("3") = queue_index; > > register long __rc asm("2"); > > + register long __cookie asm("4") = cookie; > > > > asm volatile ("diag 2,4,0x500\n" > > - : "=d" (__rc) : "d" (__nr), "d" (__schid), "d" (__index) > > + : "=d" (__rc) : "d" (__nr), "d" (__schid), "d" (__index), > > + "d"(__cookie) > > : "memory", "cc"); > > return __rc; > > } > > @@ -166,7 +170,7 @@ static void virtio_ccw_kvm_notify(struct virtqueue *vq) > > > > vcdev = to_vc_device(info->vq->vdev); > > ccw_device_get_schid(vcdev->cdev, &schid); > > - do_kvm_notify(schid, virtqueue_get_queue_index(vq)); > > + info->cookie = do_kvm_notify(schid, virtqueue_get_queue_index(vq), info->cookie); > > } > > > > static int virtio_ccw_read_vq_conf(struct virtio_ccw_device *vcdev, > > > Hmmm, forget my last mail. This actually could be even forward and backward compatible. > In the virtio spec we will not define the cookie format (just 64bit int). That will allow > qemu or future kernels to use that for other things (as long as a validity check is > possible) if we dont have a kvm bus. > > Now: > > old guest, old host: > works. > > old guest, new host: > the cookie from the guest contains junk, the host needs to detect that the cookie is > junk and ignores it. It will return the new cookie anyway. > > new guest, old host: > The guest will get a junk cookie and pass it back to the host. But the host will ignore > it anyway. > > new guest, new host: > works. > > So... > Acked-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> Yes, that sounds sane; I'll give it a try later. However, I'd rather not want to rush this; I'd prefer to get the initial version in first. I'll do a v4 later. -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html