Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932613AbdIRJbT (ORCPT ); Mon, 18 Sep 2017 05:31:19 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:56342 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754436AbdIRJP4 (ORCPT ); Mon, 18 Sep 2017 05:15:56 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jason Wang , "David S. Miller" Subject: [PATCH 4.9 20/78] vhost_net: correctly check tx avail during rx busy polling Date: Mon, 18 Sep 2017 11:11:29 +0200 Message-Id: <20170918091129.210820626@linuxfoundation.org> X-Mailer: git-send-email 2.14.1 In-Reply-To: <20170918091126.077483037@linuxfoundation.org> References: <20170918091126.077483037@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1597 Lines: 47 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jason Wang [ Upstream commit 8b949bef9172ca69d918e93509a4ecb03d0355e0 ] We check tx avail through vhost_enable_notify() in the past which is wrong since it only checks whether or not guest has filled more available buffer since last avail idx synchronization which was just done by vhost_vq_avail_empty() before. What we really want is checking pending buffers in the avail ring. Fix this by calling vhost_vq_avail_empty() instead. This issue could be noticed by doing netperf TCP_RR benchmark as client from guest (but not host). With this fix, TCP_RR from guest to localhost restores from 1375.91 trans per sec to 55235.28 trans per sec on my laptop (Intel(R) Core(TM) i7-5600U CPU @ 2.60GHz). Fixes: 030881372460 ("vhost_net: basic polling support") Signed-off-by: Jason Wang Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- drivers/vhost/net.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -537,8 +537,13 @@ static int vhost_net_rx_peek_head_len(st preempt_enable(); - if (vhost_enable_notify(&net->dev, vq)) + if (!vhost_vq_avail_empty(&net->dev, vq)) vhost_poll_queue(&vq->poll); + else if (unlikely(vhost_enable_notify(&net->dev, vq))) { + vhost_disable_notify(&net->dev, vq); + vhost_poll_queue(&vq->poll); + } + mutex_unlock(&vq->mutex); len = peek_head_len(sk);