From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH net-next] tuntap: introduce tx skb ring Date: Wed, 18 May 2016 11:23:56 +0300 Message-ID: <20160518112225-mutt-send-email-mst@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> <20160518101359.37f5343b@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Jason Wang , Eric Dumazet , davem@davemloft.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Steven Rostedt To: Jesper Dangaard Brouer Return-path: Content-Disposition: inline In-Reply-To: <20160518101359.37f5343b@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Wed, May 18, 2016 at 10:13:59AM +0200, Jesper Dangaard Brouer wrote: > On Mon, 16 May 2016 15:51:48 +0800 > Jason Wang wrote: >=20 > > 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 pro= ducer > > >> 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 cas= es, > > > 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 m= ore > > > flexibility (like the number of slots) > > > =20 > >=20 > > Yes, this sounds good. >=20 > 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 i= s > 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. >=20 > 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 >=20 > 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. >=20 > 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". >=20 >=20 > Maybe Steven Rostedt have an even better ring queue implementation > already avail in the kernel? BTW at least for tun, index based isn't really needed. A simple array seems to be more readable, faster and use less memory. I have implemented this and it seems to work OK, will post shortly. > --=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