"Michael S. Tsirkin" <m...@redhat.com> writes:
> 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 <m...@redhat.com>
> Reported-by: Edivaldo de Araujo Pereira <edivaldoapere...@yahoo.com.br>
> Tested-by: Edivaldo de Araujo Pereira <edivaldoapere...@yahoo.com.br>
> Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
> ---
>
> Anthony says he wants to test this, I only compiled this patch.
I tested it and it works.
Applied. Thanks.
Regards,
Anthony Liguori
>
> hw/virtio-rng.c | 12 +++++++++---
> hw/virtio-serial-bus.c | 2 +-
> hw/virtio.c | 15 ++++++++-------
> hw/virtio.h | 3 ++-
> 4 files changed, 20 insertions(+), 12 deletions(-)
>
> diff --git a/hw/virtio-rng.c b/hw/virtio-rng.c
> index df329f2..a73ef8e 100644
> --- a/hw/virtio-rng.c
> +++ b/hw/virtio-rng.c
> @@ -43,11 +43,11 @@ static bool is_guest_ready(VirtIORNG *vrng)
> return false;
> }
>
> -static size_t get_request_size(VirtQueue *vq)
> +static size_t get_request_size(VirtQueue *vq, unsigned quota)
> {
> unsigned int in, out;
>
> - virtqueue_get_avail_bytes(vq, &in, &out);
> + virtqueue_get_avail_bytes(vq, &in, &out, quota, 0);
> return in;
> }
>
> @@ -84,12 +84,18 @@ static void chr_read(void *opaque, const void *buf,
> size_t size)
> static void virtio_rng_process(VirtIORNG *vrng)
> {
> size_t size;
> + unsigned quota;
>
> if (!is_guest_ready(vrng)) {
> return;
> }
>
> - size = get_request_size(vrng->vq);
> + if (vrng->quota_remaining < 0) {
> + quota = 0;
> + } else {
> + quota = MIN((uint64_t)vrng->quota_remaining, (uint64_t)UINT32_MAX);
> + }
> + size = get_request_size(vrng->vq, quota);
> size = MIN(vrng->quota_remaining, size);
> if (size) {
> rng_backend_request_entropy(vrng->rng, size, chr_read, vrng);
> diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c
> index efa8a81..155da58 100644
> --- a/hw/virtio-serial-bus.c
> +++ b/hw/virtio-serial-bus.c
> @@ -306,7 +306,7 @@ 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, 4096, 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 df8d0f7..7c17f7b 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);
>
> --
> MST
