From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jesper Dangaard Brouer Subject: Re: [PATCH net-next] tuntap: introduce tx skb ring Date: Wed, 18 May 2016 10:13:59 +0200 Message-ID: <20160518101359.37f5343b@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: QUOTED-PRINTABLE Cc: brouer@redhat.com, Eric Dumazet , davem@davemloft.net, mst@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Steven Rostedt To: Jason Wang Return-path: In-Reply-To: <57397C14.1080701@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Mon, 16 May 2016 15:51:48 +0800 Jason Wang wrote: > On 2016=E5=B9=B405=E6=9C=8816=E6=97=A5 11:56, Eric Dumazet wrote: > > On Mon, 2016-05-16 at 09:17 +0800, Jason Wang wrote: =20 > >> We used to queue tx packets in sk_receive_queue, this is less > >> efficient since it requires spinlocks to synchronize between produ= cer > >> and consumer. =20 > > ... > > =20 > >> 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; > >> }; > >> =20 > > 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 mor= e > > flexibility (like the number of slots) > > =20 >=20 > 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/in= clude/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? --=20 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