From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966520AbcKKE2o (ORCPT ); Thu, 10 Nov 2016 23:28:44 -0500 Received: from mx1.redhat.com ([209.132.183.28]:53310 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965547AbcKKE2n (ORCPT ); Thu, 10 Nov 2016 23:28:43 -0500 Subject: Re: [PATCH 1/3] tuntap: rx batching To: John Fastabend , "Michael S. Tsirkin" References: <1478677113-13126-1-git-send-email-jasowang@redhat.com> <20161109183259-mutt-send-email-mst@kernel.org> <20161111053048-mutt-send-email-mst@kernel.org> <58254654.4000501@gmail.com> Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org From: Jason Wang Message-ID: <2b357b06-f749-5897-f882-aa3121e49e89@redhat.com> Date: Fri, 11 Nov 2016 12:28:38 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <58254654.4000501@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Fri, 11 Nov 2016 04:28:42 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2016年11月11日 12:17, John Fastabend wrote: > On 16-11-10 07:31 PM, Michael S. Tsirkin wrote: >> >On Fri, Nov 11, 2016 at 10:07:44AM +0800, Jason Wang wrote: >>> >> >>> >> >>> >>On 2016年11月10日 00:38, Michael S. Tsirkin wrote: >>>> >>>On Wed, Nov 09, 2016 at 03:38:31PM +0800, Jason Wang wrote: >>>>> >>>>Backlog were used for tuntap rx, but it can only process 1 packet at >>>>> >>>>one time since it was scheduled during sendmsg() synchronously in >>>>> >>>>process context. This lead bad cache utilization so this patch tries >>>>> >>>>to do some batching before call rx NAPI. This is done through: >>>>> >>>> >>>>> >>>>- accept MSG_MORE as a hint from sendmsg() caller, if it was set, >>>>> >>>> batch the packet temporarily in a linked list and submit them all >>>>> >>>> once MSG_MORE were cleared. >>>>> >>>>- implement a tuntap specific NAPI handler for processing this kind of >>>>> >>>> possible batching. (This could be done by extending backlog to >>>>> >>>> support skb like, but using a tun specific one looks cleaner and >>>>> >>>> easier for future extension). >>>>> >>>> >>>>> >>>>Signed-off-by: Jason Wang >>>> >>>So why do we need an extra queue? >>> >> >>> >>The idea was borrowed from backlog to allow some kind of bulking and avoid >>> >>spinlock on each dequeuing. >>> >> >>>> >>> This is not what hardware devices do. >>>> >>>How about adding the packet to queue unconditionally, deferring >>>> >>>signalling until we get sendmsg without MSG_MORE? >>> >> >>> >>Then you need touch spinlock when dequeuing each packet. >> > > Random thought, I have a cmpxchg ring I am using for the qdisc work that > could possibly replace the spinlock implementation. I haven't figured > out the resizing API yet because I did not need it but I assume it could > help here and let you dequeue multiple skbs in one operation. > > I can post the latest version if useful or an older version is > somewhere on patchworks as well. > > .John > > Look useful here, and I can compare the performance if you post. A question is can we extend the skb_array to support that? Thanks