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author | Vincenzo Maffione <v.maffione@gmail.com> | 2016-01-31 11:29:04 +0100 |
---|---|---|
committer | Timothy Pearson <tpearson@raptorengineering.com> | 2019-11-29 19:31:48 -0600 |
commit | 681278ab7da81e8cef464b0faa52dec0d4fa35ab (patch) | |
tree | c3cd735ddfb548e7d43fb631223f38cca10ac342 | |
parent | 38a9b5a2ff72cf727cc69b308d5d910b78f9b659 (diff) | |
download | hqemu-681278ab7da81e8cef464b0faa52dec0d4fa35ab.zip hqemu-681278ab7da81e8cef464b0faa52dec0d4fa35ab.tar.gz |
virtio: cache used_idx in a VirtQueue field
Accessing used_idx in the VQ requires an expensive access to
guest physical memory. Before this patch, 3 accesses are normally
done for each pop/push/notify call. However, since the used_idx is
only written by us, we can track it in our internal data structure.
Signed-off-by: Vincenzo Maffione <v.maffione@gmail.com>
Message-Id: <3d062ec54e9a7bf9fb325c1fd693564951f2b319.1450218353.git.v.maffione@gmail.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
-rw-r--r-- | hw/virtio/virtio.c | 12 |
1 files changed, 9 insertions, 3 deletions
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c index 225ee6d..82e6414 100644 --- a/hw/virtio/virtio.c +++ b/hw/virtio/virtio.c @@ -71,6 +71,9 @@ struct VirtQueue { VRing vring; uint16_t last_avail_idx; + + uint16_t used_idx; + /* Last used index value we have signalled on */ uint16_t signalled_used; @@ -170,6 +173,7 @@ static inline void vring_used_idx_set(VirtQueue *vq, uint16_t val) hwaddr pa; pa = vq->vring.used + offsetof(VRingUsed, idx); virtio_stw_phys(vq->vdev, pa, val); + vq->used_idx = val; } static inline void vring_used_flags_set_bit(VirtQueue *vq, int mask) @@ -261,7 +265,7 @@ void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem, virtqueue_unmap_sg(vq, elem, len); - idx = (idx + vring_used_idx(vq)) % vq->vring.num; + idx = (idx + vq->used_idx) % vq->vring.num; /* Get a pointer to the next entry in the used ring. */ vring_used_ring_id(vq, idx, elem->index); @@ -274,7 +278,7 @@ void virtqueue_flush(VirtQueue *vq, unsigned int count) /* Make sure buffer is written before we update index. */ smp_wmb(); trace_virtqueue_flush(vq, count); - old = vring_used_idx(vq); + old = vq->used_idx; new = old + count; vring_used_idx_set(vq, new); vq->inuse -= count; @@ -782,6 +786,7 @@ void virtio_reset(void *opaque) vdev->vq[i].vring.avail = 0; vdev->vq[i].vring.used = 0; vdev->vq[i].last_avail_idx = 0; + vdev->vq[i].used_idx = 0; virtio_queue_set_vector(vdev, i, VIRTIO_NO_VECTOR); vdev->vq[i].signalled_used = 0; vdev->vq[i].signalled_used_valid = false; @@ -1161,7 +1166,7 @@ static bool vring_notify(VirtIODevice *vdev, VirtQueue *vq) v = vq->signalled_used_valid; vq->signalled_used_valid = true; old = vq->signalled_used; - new = vq->signalled_used = vring_used_idx(vq); + new = vq->signalled_used = vq->used_idx; return !v || vring_need_event(vring_get_used_event(vq), new, old); } @@ -1573,6 +1578,7 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f, int version_id) vdev->vq[i].last_avail_idx, nheads); return -1; } + vdev->vq[i].used_idx = vring_used_idx(&vdev->vq[i]); } } |