From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753828AbdJaQgE (ORCPT ); Tue, 31 Oct 2017 12:36:04 -0400 Received: from mx1.redhat.com ([209.132.183.28]:32840 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753620AbdJaQgC (ORCPT ); Tue, 31 Oct 2017 12:36:02 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 60FCB7E384 Authentication-Results: ext-mx04.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx04.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=mst@redhat.com Date: Tue, 31 Oct 2017 18:36:00 +0200 From: "Michael S. Tsirkin" To: Jason Wang Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Wei Xu , Matthew Rosato Subject: Re: [PATCH net-next] vhost_net: conditionally enable tx polling Message-ID: <20171031182637-mutt-send-email-mst@kernel.org> References: <1509445640-4085-1-git-send-email-jasowang@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1509445640-4085-1-git-send-email-jasowang@redhat.com> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Tue, 31 Oct 2017 16:36:02 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 31, 2017 at 06:27:20PM +0800, Jason Wang wrote: > We always poll tx for socket, this is sub optimal since: > > - we only want to be notified when sndbuf is available > - this will slightly increase the waitqueue traversing time and more > important, vhost could not benefit from commit > commit 9e641bdcfa4e > ("net-tun: restructure tun_do_read for better sleep/wakeup efficiency") > even if we've stopped rx polling during handle_rx() since tx poll > were still left in the waitqueue. > > Pktgen from a remote host to VM over mlx4 shows 5.5% improvements on > rx PPS. (from 1.27Mpps to 1.34Mpps) > > Cc: Wei Xu > Cc: Matthew Rosato > Signed-off-by: Jason Wang > --- Now that vhost_poll_stop happens on data path a lot, I'd say if (poll->wqh) there should be unlikely(). > drivers/vhost/net.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index 68677d9..286c3e4 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -471,6 +471,7 @@ static void handle_tx(struct vhost_net *net) > goto out; > > vhost_disable_notify(&net->dev, vq); > + vhost_net_disable_vq(net, vq); > > hdr_size = nvq->vhost_hlen; > zcopy = nvq->ubufs; > @@ -556,6 +557,8 @@ static void handle_tx(struct vhost_net *net) > % UIO_MAXIOV; > } > vhost_discard_vq_desc(vq, 1); > + if (err == -EAGAIN) > + vhost_net_enable_vq(net, vq); > break; > } > if (err != len) I would probably just enable it unconditionally here. Why not? > @@ -1145,9 +1148,11 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd) > r = vhost_vq_init_access(vq); > if (r) > goto err_used; > - r = vhost_net_enable_vq(n, vq); > - if (r) > - goto err_used; > + if (index == VHOST_NET_VQ_RX) { > + r = vhost_net_enable_vq(n, vq); > + if (r) > + goto err_used; > + } > > oldubufs = nvq->ubufs; > nvq->ubufs = ubufs; This last chunk seems questionable. If queue has stuff in it when we connect the backend, we'll miss a wakeup. I suspect this can happen during migration. > -- > 2.7.4