From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH] vhost: batch used descriptors chains write-back with packed ring Date: Wed, 12 Dec 2018 13:53:58 -0500 Message-ID: <20181212134459-mutt-send-email-mst@kernel.org> References: <20181212082403.12002-1-maxime.coquelin@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Ilya Maximets , dev@dpdk.org, tiwei.bie@intel.com, zhihong.wang@intel.com, jfreimann@redhat.com, Jason Wang To: Maxime Coquelin Return-path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by dpdk.org (Postfix) with ESMTP id 7CE471B419 for ; Wed, 12 Dec 2018 19:54:03 +0100 (CET) Content-Disposition: inline In-Reply-To: List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On Wed, Dec 12, 2018 at 05:34:31PM +0100, Maxime Coquelin wrote: > Hi Ilya, > > On 12/12/18 4:23 PM, Ilya Maximets wrote: > > On 12.12.2018 11:24, Maxime Coquelin wrote: > > > Instead of writing back descriptors chains in order, let's > > > write the first chain flags last in order to improve batching. > > > > > > With Kernel's pktgen benchmark, ~3% performance gain is measured. > > > > > > Signed-off-by: Maxime Coquelin > > > --- > > > lib/librte_vhost/virtio_net.c | 39 +++++++++++++++++++++-------------- > > > 1 file changed, 24 insertions(+), 15 deletions(-) > > > > > > > Hi. > > I made some rough testing on my ARMv8 system with this patch and v1 of it. > > Here is the performance difference with current master: > > v1: +1.1 % > > v2: -3.6 % > > > > So, write barriers are quiet heavy in practice. > > Thanks for testing it on ARM. Indeed, SMP WMB is heavier on ARM. Besides your ideas for improving packed rings, maybe we should switch to load_acquite/store_release? See virtio: use smp_load_acquire/smp_store_release which worked fine but as I only tested on x86 did not result in any gains. -- MST