From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by dpdk.org (Postfix) with ESMTP id 3AE5B1B123; Wed, 24 Oct 2018 12:51:57 +0200 (CEST) Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 95FC39B2F5; Wed, 24 Oct 2018 10:51:56 +0000 (UTC) Received: from [10.36.112.57] (ovpn-112-57.ams2.redhat.com [10.36.112.57]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A5FDA5DA67; Wed, 24 Oct 2018 10:51:44 +0000 (UTC) To: dev@dpdk.org, tiwei.bie@intel.com, jfreimann@redhat.com, zhihong.wang@intel.com Cc: stable@dpdk.org References: <20181023100710.14739-1-maxime.coquelin@redhat.com> From: Maxime Coquelin Message-ID: <82847dae-6dd6-8841-f140-5b91e33c04d7@redhat.com> Date: Wed, 24 Oct 2018 12:51:22 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20181023100710.14739-1-maxime.coquelin@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Wed, 24 Oct 2018 10:51:56 +0000 (UTC) Subject: Re: [dpdk-stable] [PATCH v2] vhost: avoid memory barriers when no descriptors dequeued X-BeenThere: stable@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches for DPDK stable branches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 24 Oct 2018 10:51:57 -0000 On 10/23/18 12:07 PM, Maxime Coquelin wrote: > In both split and packed dequeue paths, flush_shadow_used_ring > and vhost_ring_call variants gets called even if not packets > have been dequeued, and so no descriptors updates happened. > > It has an impact on CPU pipeline, as memory barriers are used > in these functions. > > This patch don't call these functions if no descriptors have > been dequeued. The performance gain with split ring when > dequeue zero-copy is disabled should be null, but should be > noticeable with packed ring or dequeue zero-copy enabled. > > Fixes: ae999ce49dcb ("vhost: add Tx support for packed ring") > Fixes: 915cf9404225 ("vhost: use shadow used ring in dequeue path") > Cc:stable@dpdk.org > > Signed-off-by: Maxime Coquelin > --- > > Changes in v2: > - Fix shadow_used_idx reset in error path (Tiwei) > > lib/librte_vhost/virtio_net.c | 24 ++++++++++++++++-------- > 1 file changed, 16 insertions(+), 8 deletions(-) Applied to dpdk-next-virtio/master. Maxime