2010/12/24 Michael S. Tsirkin <mst@xxxxxxxxxx>:
> On Fri, Dec 24, 2010 at 10:14:50PM +0900, Yoshiaki Tamura wrote:
>> 2010/12/24 Michael S. Tsirkin <mst@xxxxxxxxxx>:
>> > On Fri, Dec 24, 2010 at 08:22:00PM +0900, Yoshiaki Tamura wrote:
>> >> 2010/12/24 Michael S. Tsirkin <mst@xxxxxxxxxx>:
>> >> > On Fri, Dec 24, 2010 at 12:18:15PM +0900, Yoshiaki Tamura wrote:
>> >> >> virtio save/load is currently sending last_avail_idx, but inuse isn't.
>> >> >> This causes inconsistent state when using Kemari which replays
>> >> >> outstanding requests on the secondary. By letting last_avail_idx to
>> >> >> be updated after inuse is decreased, it would be possible to replay
>> >> >> the outstanding requests. Noth that live migration shouldn't be
>> >> >> affected because it waits until flushing all requests. Also in
>> >> >> conjunction with event-tap, requests inversion should be avoided.
>> >> >>
>> >> >> Signed-off-by: Yoshiaki Tamura <tamura.yoshiaki@xxxxxxxxxxxxx>
>> >> >
>> >> > I think I understood the request inversion. My question now is,
>> >> > event-tap transfers inuse events as well, wont the same
>> >> > request be repeated twice?
>> >> >
>> >> >> ---
>> >> >> hw/virtio.c | 8 +++++++-
>> >> >> 1 files changed, 7 insertions(+), 1 deletions(-)
>> >> >>
>> >> >> diff --git a/hw/virtio.c b/hw/virtio.c
>> >> >> index 07dbf86..f915c46 100644
>> >> >> --- a/hw/virtio.c
>> >> >> +++ b/hw/virtio.c
>> >> >> @@ -72,7 +72,7 @@ struct VirtQueue
>> >> >> VRing vring;
>> >> >> target_phys_addr_t pa;
>> >> >> uint16_t last_avail_idx;
>> >> >> - int inuse;
>> >> >> + uint16_t inuse;
>> >> >> uint16_t vector;
>> >> >> void (*handle_output)(VirtIODevice *vdev, VirtQueue *vq);
>> >> >> VirtIODevice *vdev;
>> >> >> @@ -671,6 +671,7 @@ void virtio_save(VirtIODevice *vdev, QEMUFile *f)
>> >> >> qemu_put_be32(f, vdev->vq[i].vring.num);
>> >> >> qemu_put_be64(f, vdev->vq[i].pa);
>> >> >> qemu_put_be16s(f, &vdev->vq[i].last_avail_idx);
>> >> >> + qemu_put_be16s(f, &vdev->vq[i].inuse);
>> >> >> if (vdev->binding->save_queue)
>> >> >> vdev->binding->save_queue(vdev->binding_opaque, i, f);
>> >> >> }
>> >> >> @@ -710,6 +711,11 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f)
>> >> >> vdev->vq[i].vring.num = qemu_get_be32(f);
>> >> >> vdev->vq[i].pa = qemu_get_be64(f);
>> >> >> qemu_get_be16s(f, &vdev->vq[i].last_avail_idx);
>> >> >> + qemu_get_be16s(f, &vdev->vq[i].inuse);
>> >> >> +
>> >> >> + /* revert last_avail_idx if there are outstanding emulation. */
>> >> >
>> >> > if there are outstanding emulation -> if requests
>> >> > are outstanding in event-tap?
>> >> >
>> >> >> + vdev->vq[i].last_avail_idx -= vdev->vq[i].inuse;
>> >> >> + vdev->vq[i].inuse = 0;
>> >> >>
>> >> >
>> >> > I don't understand it, if this is all we do we can equivalently
>> >> > decrement on the sender side and avoid breaking migration compatibility?
>> >>
>> >> It seems I sent the old patch... I'm really sorry. Currently
>> >> I'm taking the approach to update last_avai_idx later.
>> >> Decreasing looks scary to me if the guest already knows about it.
>> >
>> > It seems exactly the same functionally.
>>
>> If it is the same I'm fine to go with the decreasing approach.
>> Is it fine for the guest? Is last_avai_idx irrelevant to the
>> guest's behavior?
>>
>> Yoshi
>
> At least at the moment, yes.
OK. I'll put it in the next spin. Thanks for your advices!
Yoshi
>
>> >> commit 8ac6ba51cc558b3bfcac7a5814d92f275ee874e9
>> >> Author: Yoshiaki Tamura <tamura.yoshiaki@xxxxxxxxxxxxx>
>> >> Date: Mon May 17 10:36:14 2010 +0900
>> >>
>> >> virtio: update last_avail_idx when inuse is decreased.
>> >>
>> >> virtio save/load is currently sending last_avail_idx, but inuse isn't.
>> >> This causes inconsistent state when using Kemari which replays
>> >> outstanding requests on the secondary. By letting last_avail_idx to
>> >> be updated after inuse is decreased, it would be possible to replay
>> >> the outstanding requests. Noth that live migration shouldn't be
>> >> affected because it waits until flushing all requests. Also in
>> >> conjunction with event-tap, requests inversion should be avoided.
>> >>
>> >> Signed-off-by: Yoshiaki Tamura <tamura.yoshiaki@xxxxxxxxxxxxx>
>> >>
>> >> diff --git a/hw/virtio.c b/hw/virtio.c
>> >> index 07dbf86..b1586da 100644
>> >> --- a/hw/virtio.c
>> >> +++ b/hw/virtio.c
>> >> @@ -198,7 +198,7 @@ int virtio_queue_ready(VirtQueue *vq)
>> >>
>> >> int virtio_queue_empty(VirtQueue *vq)
>> >> {
>> >> - return vring_avail_idx(vq) == vq->last_avail_idx;
>> >> + return vring_avail_idx(vq) == vq->last_avail_idx + vq->inuse;
>> >> }
>> >>
>> >> void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
>> >> @@ -238,6 +238,7 @@ void virtqueue_flush(VirtQueue *vq, unsigned int count)
>> >> wmb();
>> >> trace_virtqueue_flush(vq, count);
>> >> vring_used_idx_increment(vq, count);
>> >> + vq->last_avail_idx += count;
>> >> vq->inuse -= count;
>> >> }
>> >>
>> >> @@ -306,7 +307,7 @@ int virtqueue_avail_bytes(VirtQueue *vq, int in_bytes, int o
>> >> unsigned int idx;
>> >> int total_bufs, in_total, out_total;
>> >>
>> >> - idx = vq->last_avail_idx;
>> >> + idx = vq->last_avail_idx + vq->inuse;
>> >>
>> >> total_bufs = in_total = out_total = 0;
>> >> while (virtqueue_num_heads(vq, idx)) {
>> >> @@ -386,7 +387,7 @@ int virtqueue_pop(VirtQueue *vq, VirtQueueElement *elem)
>> >> unsigned int i, head, max;
>> >> target_phys_addr_t desc_pa = vq->vring.desc;
>> >>
>> >> - if (!virtqueue_num_heads(vq, vq->last_avail_idx))
>> >> + if (!virtqueue_num_heads(vq, vq->last_avail_idx + vq->inuse))
>> >> return 0;
>> >>
>> >> /* When we start there are none of either input nor output. */
>> >> @@ -394,7 +395,7 @@ int virtqueue_pop(VirtQueue *vq, VirtQueueElement *elem)
>> >>
>> >> max = vq->vring.num;
>> >>
>> >> - i = head = virtqueue_get_head(vq, vq->last_avail_idx++);
>> >> + i = head = virtqueue_get_head(vq, vq->last_avail_idx + vq->inuse);
>> >>
>> >> if (vring_desc_flags(desc_pa, i) & VRING_DESC_F_INDIRECT) {
>> >> if (vring_desc_len(desc_pa, i) % sizeof(VRingDesc)) {
>> >> @@ -626,7 +627,7 @@ void virtio_notify(VirtIODevice *vdev, VirtQueue *vq)
>> >> /* Always notify when queue is empty (when feature acknowledge) */
>> >> if ((vring_avail_flags(vq) & VRING_AVAIL_F_NO_INTERRUPT) &&
>> >> (!(vdev->guest_features & (1 << VIRTIO_F_NOTIFY_ON_EMPTY)) ||
>> >> - (vq->inuse || vring_avail_idx(vq) != vq->last_avail_idx)))
>> >> + (vq->inuse || vring_avail_idx(vq) != vq->last_avail_idx + vq->inuse)))
>> >> return;
>> >>
>> >> trace_virtio_notify(vdev, vq);
>> >>
>> >>
>> >> >
>> >> >> if (vdev->vq[i].pa) {
>> >> >> uint16_t nheads;
>> >> >> --
>> >> >> 1.7.1.2
>> >> > --
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>> >
>
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