From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753276AbcERKXz (ORCPT ); Wed, 18 May 2016 06:23:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56322 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751169AbcERKXx (ORCPT ); Wed, 18 May 2016 06:23:53 -0400 Subject: Re: [PATCH net-next] tuntap: introduce tx skb ring To: Jesper Dangaard Brouer References: <1463361421-4397-1-git-send-email-jasowang@redhat.com> <1463370998.18194.74.camel@edumazet-glaptop3.roam.corp.google.com> <57397C14.1080701@redhat.com> <20160518101359.37f5343b@redhat.com> Cc: Eric Dumazet , davem@davemloft.net, mst@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Steven Rostedt From: Jason Wang Message-ID: <573C42B4.6040708@redhat.com> Date: Wed, 18 May 2016 18:23:48 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.2 MIME-Version: 1.0 In-Reply-To: <20160518101359.37f5343b@redhat.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 [10.5.110.30]); Wed, 18 May 2016 10:23:53 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2016年05月18日 16:13, Jesper Dangaard Brouer wrote: > On Mon, 16 May 2016 15:51:48 +0800 > Jason Wang wrote: > >> On 2016年05月16日 11:56, Eric Dumazet wrote: >>> On Mon, 2016-05-16 at 09:17 +0800, Jason Wang wrote: >>>> We used to queue tx packets in sk_receive_queue, this is less >>>> efficient since it requires spinlocks to synchronize between producer >>>> and consumer. >>> ... >>> >>>> struct tun_struct *detached; >>>> + /* reader lock */ >>>> + spinlock_t rlock; >>>> + unsigned long tail; >>>> + struct tun_desc tx_descs[TUN_RING_SIZE]; >>>> + /* writer lock */ >>>> + spinlock_t wlock; >>>> + unsigned long head; >>>> }; >>>> >>> Ok, we had these kind of ideas floating around for many other cases, >>> like qdisc, UDP or af_packet sockets... >>> >>> I believe we should have a common set of helpers, not hidden in >>> drivers/net/tun.c but in net/core/skb_ring.c or something, with more >>> flexibility (like the number of slots) >>> >> Yes, this sounds good. > I agree. It is sad to see everybody is implementing the same thing, > open coding an array/circular based ring buffer. This kind of code is > hard to maintain and get right with barriers etc. We can achieve the > same performance with a generic implementation, by inlining the help > function calls. > > I implemented an array based Lock-Free/cmpxchg based queue, that you > could be inspired by, see: > https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/include/linux/alf_queue.h This looks really interesting, thanks. > > The main idea behind my implementation is bulking, to amortize the > locked cmpxchg operation. You might not need it now, but I expect we > need it in the future. Right, we need change APIs which can read or write multiple buffers at one time for tun (and for others). I agree this will be a good optimization in the future. > > You cannot use my alf_queue directly as your "struct tun_desc" is > larger than one-pointer (which the alf_queue works with). But it > should be possible to extend to handle larger "objects". Yes, and for more generic usage, maybe one more void * is sufficient. > > > Maybe Steven Rostedt have an even better ring queue implementation > already avail in the kernel? > You mean ring buffer in tracing? Not sure, but it looks rather complex at first glance.