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 <jasow...@redhat.com> 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?
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. > -- > 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
