From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966370AbcKKEKu (ORCPT ); Thu, 10 Nov 2016 23:10:50 -0500 Received: from mx1.redhat.com ([209.132.183.28]:50866 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965625AbcKKEKt (ORCPT ); Thu, 10 Nov 2016 23:10:49 -0500 Subject: Re: [PATCH 1/3] tuntap: rx batching To: "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> Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org From: Jason Wang Message-ID: Date: Fri, 11 Nov 2016 12:10:44 +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: <20161111053048-mutt-send-email-mst@kernel.org> 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 04:10:48 +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 11:31, 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. > It runs on the same CPU, right? Otherwise we should use skb_array... > There could be multiple senders technically. Will try skb_array and see if there's any difference. Thanks