"Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote on 01/28/2011 06:16:16 AM:
> OK, so thinking about it more, maybe the issue is this:
> tx becomes full. We process one request and interrupt the guest,
> then it adds one request and the queue is full again.
>
> Maybe the following will help it stabilize?
> By itself it does nothing, but if you set
> all the parameters to a huge value we will
> only interrupt when we see an empty ring.
> Which might be too much: pls try other values
> in the middle: e.g. make bufs half the ring,
> or bytes some small value, or packets some
> small value etc.
>
> Warning: completely untested.
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index aac05bc..6769cdc 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -32,6 +32,13 @@
> * Using this limit prevents one virtqueue from starving others. */
> #define VHOST_NET_WEIGHT 0x80000
>
> +int tx_bytes_coalesce = 0;
> +module_param(tx_bytes_coalesce, int, 0644);
> +int tx_bufs_coalesce = 0;
> +module_param(tx_bufs_coalesce, int, 0644);
> +int tx_packets_coalesce = 0;
> +module_param(tx_packets_coalesce, int, 0644);
> +
> enum {
> VHOST_NET_VQ_RX = 0,
> VHOST_NET_VQ_TX = 1,
> @@ -127,6 +134,9 @@ static void handle_tx(struct vhost_net *net)
> int err, wmem;
> size_t hdr_size;
> struct socket *sock;
> + int bytes_coalesced = 0;
> + int bufs_coalesced = 0;
> + int packets_coalesced = 0;
>
> /* TODO: check that we are running from vhost_worker? */
> sock = rcu_dereference_check(vq->private_data, 1);
> @@ -196,14 +206,26 @@ static void handle_tx(struct vhost_net *net)
> if (err != len)
> pr_debug("Truncated TX packet: "
> " len %d != %zd\n", err, len);
> - vhost_add_used_and_signal(&net->dev, vq, head, 0);
> total_len += len;
> + packets_coalesced += 1;
> + bytes_coalesced += len;
> + bufs_coalesced += in;
Should this instead be:
bufs_coalesced += out;
Perusing the code I see that earlier there is a check to see if "in" is not
zero, and, if so, error out of the loop. After the check, "in" is not
touched until it is added to bufs_coalesced, effectively not changing
bufs_coalesced, meaning bufs_coalesced will never trigger the conditions
below.
Or am I missing something?
> + if (unlikely(packets_coalesced > tx_packets_coalesce ||
> + bytes_coalesced > tx_bytes_coalesce ||
> + bufs_coalesced > tx_bufs_coalesce))
> + vhost_add_used_and_signal(&net->dev, vq, head, 0);
> + else
> + vhost_add_used(vq, head, 0);
> if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
> vhost_poll_queue(&vq->poll);
> break;
> }
> }
>
> + if (likely(packets_coalesced > tx_packets_coalesce ||
> + bytes_coalesced > tx_bytes_coalesce ||
> + bufs_coalesced > tx_bufs_coalesce))
> + vhost_signal(&net->dev, vq);
> mutex_unlock(&vq->mutex);
> }
>
Steve D.
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