From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shirley Ma Subject: Re: [PATCH net-next]vhost: fix condition check for # of outstanding dma buffers Date: Tue, 19 Jul 2011 13:56:25 -0700 Message-ID: <1311108985.8573.30.camel@localhost.localdomain> References: <1311100678.8573.16.camel@localhost.localdomain> <20110719190945.GB8667@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: David Miller , netdev@vger.kernel.org, jasowang@redhat.com To: "Michael S. Tsirkin" Return-path: Received: from e33.co.us.ibm.com ([32.97.110.151]:49802 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751924Ab1GSU4d (ORCPT ); Tue, 19 Jul 2011 16:56:33 -0400 Received: from d03relay02.boulder.ibm.com (d03relay02.boulder.ibm.com [9.17.195.227]) by e33.co.us.ibm.com (8.14.4/8.13.1) with ESMTP id p6JKmnDG011621 for ; Tue, 19 Jul 2011 14:48:49 -0600 Received: from d03av01.boulder.ibm.com (d03av01.boulder.ibm.com [9.17.195.167]) by d03relay02.boulder.ibm.com (8.13.8/8.13.8/NCO v9.1) with ESMTP id p6JKuRkD189388 for ; Tue, 19 Jul 2011 14:56:28 -0600 Received: from d03av01.boulder.ibm.com (loopback [127.0.0.1]) by d03av01.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p6JKuR89013967 for ; Tue, 19 Jul 2011 14:56:27 -0600 In-Reply-To: <20110719190945.GB8667@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, 2011-07-19 at 22:09 +0300, Michael S. Tsirkin wrote: > On Tue, Jul 19, 2011 at 11:37:58AM -0700, Shirley Ma wrote: > > Signed-off-by: Shirley Ma > > --- > > > > drivers/vhost/net.c | 6 ++++-- > > 1 files changed, 4 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > > index 70ac604..83cb738 100644 > > --- a/drivers/vhost/net.c > > +++ b/drivers/vhost/net.c > > @@ -189,8 +189,10 @@ static void handle_tx(struct vhost_net *net) > > break; > > } > > /* If more outstanding DMAs, queue the work */ > > - if (unlikely(vq->upend_idx - vq->done_idx > > > - VHOST_MAX_PEND)) { > > + if (unlikely((vq->upend_idx - vq->done_idx > > > + VHOST_MAX_PEND) || > > + (vq->upend_idx - vq->done_idx > > > + VHOST_MAX_PEND - > UIO_MAXIOV))) { > > Could you please explain why this makes sense please? > VHOST_MAX_PEND is 128 UIO_MAXIOV is 1024 so > the result is negative? I thought it is equal to: if (vq->upend_idx > vq->done_idx) check vq->upend_idx - vq->done_idx > VHOST_MAX_PEND if (vq->upend_idx < vq->done_idx) check vq->upend_idx + UIO_MAXIOV - vq->done_idx > VHOST_MAX_PEND > I thought upend_idx - done_idx is exactly the number > of buffers, so once we get too many we stop until > one gets freed? They are index, so in vhost zerocopy callback, we can get the idx right away. > > > tx_poll_start(net, sock); > > set_bit(SOCK_ASYNC_NOSPACE, > &sock->flags); > > break; > >