From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752894AbcKIT5Q (ORCPT ); Wed, 9 Nov 2016 14:57:16 -0500 Received: from mx1.redhat.com ([209.132.183.28]:58236 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751618AbcKIT5O (ORCPT ); Wed, 9 Nov 2016 14:57:14 -0500 Date: Wed, 9 Nov 2016 21:57:13 +0200 From: "Michael S. Tsirkin" To: Jason Wang Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/3] vhost: better detection of available buffers Message-ID: <20161109215513-mutt-send-email-mst@kernel.org> References: <1478677113-13126-1-git-send-email-jasowang@redhat.com> <1478677113-13126-2-git-send-email-jasowang@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1478677113-13126-2-git-send-email-jasowang@redhat.com> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Wed, 09 Nov 2016 19:57:14 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 09, 2016 at 03:38:32PM +0800, Jason Wang wrote: > We should use vq->last_avail_idx instead of vq->avail_idx in the > checking of vhost_vq_avail_empty() since latter is the cached avail > index from guest but we want to know if there's pending available > buffers in the virtqueue. > > Signed-off-by: Jason Wang I'm not sure why is this patch here. Is it related to batching somehow? > --- > drivers/vhost/vhost.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index c6f2d89..fdf4cdf 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -2230,7 +2230,7 @@ bool vhost_vq_avail_empty(struct vhost_dev *dev, struct vhost_virtqueue *vq) > if (r) > return false; > > - return vhost16_to_cpu(vq, avail_idx) == vq->avail_idx; > + return vhost16_to_cpu(vq, avail_idx) == vq->last_avail_idx; > } > EXPORT_SYMBOL_GPL(vhost_vq_avail_empty); That might be OK for TX but it's probably wrong for RX where the fact that used != avail does not mean we have enough space to store the packet. Maybe we should just rename this to vhost_vq_avail_unchanged to clarify usage. > > -- > 2.7.4