Commit e1f7b481 authored by Michael S. Tsirkin's avatar Michael S. Tsirkin Committed by Anthony Liguori
Browse files

virtio: limit avail bytes lookahead 



Commit 0d8d7690 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: default avatarMichael S. Tsirkin <mst@redhat.com>
Reported-by: default avatarEdivaldo de Araujo Pereira <edivaldoapereira@yahoo.com.br>
Tested-by: default avatarEdivaldo de Araujo Pereira <edivaldoapereira@yahoo.com.br>
Reviewed-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: default avatarAnthony Liguori <aliguori@us.ibm.com>
parent 044d003d

hw/virtio-rng.c

+9 −3
Original line number Diff line number Diff line
@@ -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);

hw/virtio-serial-bus.c

+1 −1
Original line number Diff line number Diff line
@@ -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;

}

hw/virtio.c

+8 −7
Original line number Diff line number Diff line
@@ -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,

hw/virtio.h

+2 −1
Original line number Diff line number Diff line
@@ -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);