diff options
| author | Michael S. Tsirkin <mst@redhat.com> | 2012-11-30 00:02:56 +0200 |
|---|---|---|
| committer | Anthony Liguori <aliguori@us.ibm.com> | 2012-11-29 17:25:02 -0600 |
| commit | e1f7b4812eab992de46c98b3726745afb042a7f0 (patch) | |
| tree | 288ec43f0807224674026579208dc46748bcaf32 /hw/virtio.c | |
| parent | 044d003db9b6a588be2c9d0ec9de694ba3848551 (diff) | |
| download | qemu-e1f7b4812eab992de46c98b3726745afb042a7f0.zip qemu-e1f7b4812eab992de46c98b3726745afb042a7f0.tar.gz qemu-e1f7b4812eab992de46c98b3726745afb042a7f0.tar.bz2 | |
virtio: limit avail bytes lookahead
Commit 0d8d7690850eb0cf2b2b60933cf47669a6b6f18f introduced
a regression in virtio-net performance because it looks
into the ring aggressively while we really only care
about a single packet worth of buffers.
Reported as bugzilla 1066055 in launchpad.
To fix, add parameters limiting lookahead, and
use in virtqueue_avail_bytes.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reported-by: Edivaldo de Araujo Pereira <edivaldoapereira@yahoo.com.br>
Tested-by: Edivaldo de Araujo Pereira <edivaldoapereira@yahoo.com.br>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Diffstat (limited to 'hw/virtio.c')
| -rw-r--r-- | hw/virtio.c | 15 |
1 files changed, 8 insertions, 7 deletions
diff --git a/hw/virtio.c b/hw/virtio.c index ec8b7d8..f40a8c5 100644 --- a/hw/virtio.c +++ b/hw/virtio.c @@ -336,7 +336,8 @@ static unsigned virtqueue_next_desc(hwaddr desc_pa, } void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes, - unsigned int *out_bytes) + unsigned int *out_bytes, + unsigned max_in_bytes, unsigned max_out_bytes) { unsigned int idx; unsigned int total_bufs, in_total, out_total; @@ -385,6 +386,9 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes, } else { out_total += vring_desc_len(desc_pa, i); } + if (in_total >= max_in_bytes && out_total >= max_out_bytes) { + goto done; + } } while ((i = virtqueue_next_desc(desc_pa, i, max)) != max); if (!indirect) @@ -392,6 +396,7 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes, else total_bufs++; } +done: if (in_bytes) { *in_bytes = in_total; } @@ -405,12 +410,8 @@ int virtqueue_avail_bytes(VirtQueue *vq, unsigned int in_bytes, { unsigned int in_total, out_total; - virtqueue_get_avail_bytes(vq, &in_total, &out_total); - if ((in_bytes && in_bytes < in_total) - || (out_bytes && out_bytes < out_total)) { - return 1; - } - return 0; + virtqueue_get_avail_bytes(vq, &in_total, &out_total, in_bytes, out_bytes); + return in_bytes <= in_total && out_bytes <= out_total; } void virtqueue_map_sg(struct iovec *sg, hwaddr *addr, |