From: "Michael S. Tsirkin" <mst@redhat•com>
To: Sridhar Samudrala <sri@us•ibm.com>
Cc: David Miller <davem@davemloft•net>, netdev <netdev@vger•kernel.org>
Subject: Re: [PATCH net-next-2.6] vhost: Restart tx poll when socket send queue is full
Date: Fri, 19 Feb 2010 00:30:21 +0200 [thread overview]
Message-ID: <20100218223021.GB14847@redhat.com> (raw)
In-Reply-To: <1266526751.15681.71.camel@w-sridhar.beaverton.ibm.com>
On Thu, Feb 18, 2010 at 12:59:11PM -0800, Sridhar Samudrala wrote:
> When running guest to remote host TCP stream test using vhost-net
> via tap/macvtap, i am seeing network transmit hangs. This happens
> when handle_tx() returns because of the socket send queue full
> condition.
> This patch fixes this by restarting tx poll when hitting this
> condition.
Thanks! I would like to better understand what happens exactly.
Some questions below:
>
> Signed-off-by: Sridhar Samudrala <sri@us•ibm.com>
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 91a324c..82d4bbe 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -113,12 +113,16 @@ static void handle_tx(struct vhost_net *net)
> if (!sock)
> return;
>
> - wmem = atomic_read(&sock->sk->sk_wmem_alloc);
> - if (wmem >= sock->sk->sk_sndbuf)
> - return;
> -
The disadvantage here is that a spurious wakeup
when queue is still full becomes more expensive.
> use_mm(net->dev.mm);
> mutex_lock(&vq->mutex);
> +
> + wmem = atomic_read(&sock->sk->sk_wmem_alloc);
> + if (wmem >= sock->sk->sk_sndbuf) {
> + tx_poll_start(net, sock);
Hmm. We already do
if (wmem >= sock->sk->sk_sndbuf * 3 / 4) {
tx_poll_start(net, sock);
set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
break;
}
why does not this code trigger here?
> + set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
Isn't the bit already set? If not, why?
> + goto unlock;
> + }
> +
> vhost_disable_notify(vq);
>
> if (wmem < sock->sk->sk_sndbuf * 2)
> @@ -178,6 +182,7 @@ static void handle_tx(struct vhost_net *net)
> }
> }
>
> +unlock:
> mutex_unlock(&vq->mutex);
> unuse_mm(net->dev.mm);
> }
>
next prev parent reply other threads:[~2010-02-18 22:33 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-18 20:59 [PATCH net-next-2.6] vhost: Restart tx poll when socket send queue is full Sridhar Samudrala
2010-02-18 22:30 ` Michael S. Tsirkin [this message]
2010-02-19 2:00 ` Sridhar Samudrala
2010-02-19 14:42 ` Michael S. Tsirkin
2010-02-19 21:19 ` Sridhar Samudrala
2010-02-23 10:24 ` Michael S. Tsirkin
2010-02-23 17:31 ` Sridhar Samudrala
2010-02-26 3:09 ` Shirley Ma
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