From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" 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 Message-ID: <20100218223021.GB14847@redhat.com> References: <1266526751.15681.71.camel@w-sridhar.beaverton.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: David Miller , netdev To: Sridhar Samudrala Return-path: Received: from mx1.redhat.com ([209.132.183.28]:59138 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758745Ab0BRWdt (ORCPT ); Thu, 18 Feb 2010 17:33:49 -0500 Content-Disposition: inline In-Reply-To: <1266526751.15681.71.camel@w-sridhar.beaverton.ibm.com> Sender: netdev-owner@vger.kernel.org List-ID: 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 > > 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); > } >