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virtio: limit avail bytes lookahead 

Commit 0d8d769085 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>
This commit is contained in:
Michael S. Tsirkin 2012-11-30 00:02:56 +02:00 committed by Anthony Liguori
parent 044d003db9
commit e1f7b4812e
4 changed files with 20 additions and 12 deletions
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12
hw/virtio-rng.c
View File

@ -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);

2
hw/virtio-serial-bus.c
View File

@ -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;
}

15
hw/virtio.c
View File

@ -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,

3
hw/virtio.h
View File

@ -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);