Re: [PATCHv2 11/14] virtio: don't delay avail index update
From: Rusty Russell <hidden>
Date: 2011-05-21 02:34:52
Also in:
kvm, lkml
On Fri, 20 May 2011 02:12:19 +0300, "Michael S. Tsirkin" [off-list ref] wrote:
quoted hunk ↗ jump to hunk
Update avail index immediately instead of upon kick: for virtio-net RX this helps parallelism with the host. Signed-off-by: Michael S. Tsirkin <redacted> --- drivers/virtio/virtio_ring.c | 28 +++++++++++++++++++--------- 1 files changed, 19 insertions(+), 9 deletions(-)diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index eed5f29..8218fe6 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c@@ -89,7 +89,7 @@ struct vring_virtqueue unsigned int num_free; /* Head of free buffer list. */ unsigned int free_head; - /* Number we've added since last sync. */ + /* Number we've added since last kick. */ unsigned int num_added;
I always like to see obsolescent nomenclature cleaned up like this. Thanks.
quoted hunk ↗ jump to hunk
/* Last used index we've seen. */@@ -174,6 +174,13 @@ int virtqueue_add_buf_gfp(struct virtqueue *_vq, BUG_ON(data == NULL); + /* Prevent drivers from adding more than num bufs without a kick. */ + if (vq->num_added == vq->vring.num) { + printk(KERN_ERR "gaaa!!!\n"); + END_USE(vq); + return -ENOSPC; + } +
I like "gaaa!" but it won't tell us which driver. How about the more
conventional:
if (WARN_ON(vq->num_added >= vq->vring.num)) {
END_USE(vq);
return -ENOSPC;
}
I'd really like to see the results of this patch. It's useless for
outgoing net traffic (we deal with one packet at a time) but perhaps a
flood of incoming packets would show something.
Thanks,
Rusty.