From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752183AbcERIO3 (ORCPT ); Wed, 18 May 2016 04:14:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46011 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750795AbcERIOG convert rfc822-to-8bit (ORCPT ); Wed, 18 May 2016 04:14:06 -0400 Date: Wed, 18 May 2016 10:13:59 +0200 From: Jesper Dangaard Brouer To: Jason Wang Cc: brouer@redhat.com, Eric Dumazet , davem@davemloft.net, mst@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Steven Rostedt Subject: Re: [PATCH net-next] tuntap: introduce tx skb ring Message-ID: <20160518101359.37f5343b@redhat.com> In-Reply-To: <57397C14.1080701@redhat.com> References: <1463361421-4397-1-git-send-email-jasowang@redhat.com> <1463370998.18194.74.camel@edumazet-glaptop3.roam.corp.google.com> <57397C14.1080701@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Wed, 18 May 2016 08:14:05 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 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. 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". Maybe Steven Rostedt have an even better ring queue implementation already avail in the kernel? -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat Author of http://www.iptv-analyzer.org LinkedIn: http://www.linkedin.com/in/brouer