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. To fix, add parameters limiting lookahead, and use in virtqueue_avail_bytes.
Signed-off-by: Michael S. Tsirkin <m...@redhat.com> Reported-by: Edivaldo de Araujo Pereira <edivaldoapere...@yahoo.com.br> --- Edivaldo could you please confirm this fixes regression? diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c index d20bd8b..a761cdc 100644 --- a/hw/virtio-serial-bus.c +++ b/hw/virtio-serial-bus.c @@ -297,7 +297,7 @@ size_t virtio_serial_guest_ready(VirtIOSerialPort *port) if (use_multiport(port->vser) && !port->guest_connected) { return 0; } - virtqueue_get_avail_bytes(vq, &bytes, NULL); + virtqueue_get_avail_bytes(vq, &bytes, NULL, UINT_MAX, 0); return bytes; } 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, diff --git a/hw/virtio.h b/hw/virtio.h index ac482be..1278328 100644 --- a/hw/virtio.h +++ b/hw/virtio.h @@ -150,7 +150,8 @@ int virtqueue_pop(VirtQueue *vq, VirtQueueElement *elem); int virtqueue_avail_bytes(VirtQueue *vq, unsigned int in_bytes, unsigned int out_bytes); 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); void virtio_notify(VirtIODevice *vdev, VirtQueue *vq);