From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S970744AbdI0A1t (ORCPT ); Tue, 26 Sep 2017 20:27:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41296 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964956AbdI0A1q (ORCPT ); Tue, 26 Sep 2017 20:27:46 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 1C1BC356CC Authentication-Results: ext-mx06.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx06.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=jasowang@redhat.com Subject: Re: [PATCH net-next RFC 0/5] batched tx processing in vhost_net To: "Michael S. Tsirkin" Cc: virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org References: <1506067355-5771-1-git-send-email-jasowang@redhat.com> <20170926164055-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: Date: Wed, 27 Sep 2017 08:27:37 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <20170926164055-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Wed, 27 Sep 2017 00:27:46 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2017年09月26日 21:45, Michael S. Tsirkin wrote: > On Fri, Sep 22, 2017 at 04:02:30PM +0800, Jason Wang wrote: >> Hi: >> >> This series tries to implement basic tx batched processing. This is >> done by prefetching descriptor indices and update used ring in a >> batch. This intends to speed up used ring updating and improve the >> cache utilization. > Interesting, thanks for the patches. So IIUC most of the gain is really > overcoming some of the shortcomings of virtio 1.0 wrt cache utilization? Yes. Actually, looks like batching in 1.1 is not as easy as in 1.0. In 1.0, we could do something like: batch update used ring by user copy_to_user() smp_wmb() update used_idx In 1.1, we need more memory barriers, can't benefit from fast copy helpers? for () {     update desc.addr     smp_wmb()     update desc.flag } > > Which is fair enough (1.0 is already deployed) but I would like to avoid > making 1.1 support harder, and this patchset does this unfortunately, I think the new APIs do not expose more internal data structure of virtio than before? (vq->heads has already been used by vhost_net for years). Consider the layout is re-designed completely, I don't see an easy method to reuse current 1.0 API for 1.1. > see comments on individual patches. I'm sure it can be addressed though. > >> Test shows about ~22% improvement in tx pss. > Is this with or without tx napi in guest? MoonGen is used in guest for better numbers. Thanks > >> Please review. >> >> Jason Wang (5): >> vhost: split out ring head fetching logic >> vhost: introduce helper to prefetch desc index >> vhost: introduce vhost_add_used_idx() >> vhost_net: rename VHOST_RX_BATCH to VHOST_NET_BATCH >> vhost_net: basic tx virtqueue batched processing >> >> drivers/vhost/net.c | 221 ++++++++++++++++++++++++++++---------------------- >> drivers/vhost/vhost.c | 165 +++++++++++++++++++++++++++++++------ >> drivers/vhost/vhost.h | 9 ++ >> 3 files changed, 270 insertions(+), 125 deletions(-) >> >> -- >> 2.7.4