On Fri, Apr 29, 2016 at 12:10:31PM -0400, Neil Horman wrote: > On Fri, Apr 29, 2016 at 10:47:25AM -0300, marcelo.leitner@xxxxxxxxx wrote: > > On Fri, Apr 29, 2016 at 09:36:37AM -0400, Neil Horman wrote: > > > On Thu, Apr 28, 2016 at 05:46:59PM -0300, marcelo.leitner@xxxxxxxxx wrote: > > > > On Thu, Apr 14, 2016 at 05:19:00PM -0300, marcelo.leitner@xxxxxxxxx wrote: > > > > > On Thu, Apr 14, 2016 at 04:03:51PM -0400, Neil Horman wrote: > > > > > > On Thu, Apr 14, 2016 at 02:59:16PM -0400, David Miller wrote: > > > > > > > From: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx> > > > > > > > Date: Thu, 14 Apr 2016 14:00:49 -0300 > > > > > > > > > > > > > > > Em 14-04-2016 10:03, Neil Horman escreveu: > > > > > > > >> On Wed, Apr 13, 2016 at 11:05:32PM -0400, David Miller wrote: > > > > > > > >>> From: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx> > > > > > > > >>> Date: Fri, 8 Apr 2016 16:41:26 -0300 > > > > > > > >>> > > > > > > > >>>> 1st patch is a preparation for the 2nd. The idea is to not call > > > > > > > >>>> ->sk_data_ready() for every data chunk processed while processing > > > > > > > >>>> packets but only once before releasing the socket. > > > > > > > >>>> > > > > > > > >>>> v2: patchset re-checked, small changelog fixes > > > > > > > >>>> v3: on patch 2, make use of local vars to make it more readable > > > > > > > >>> > > > > > > > >>> Applied to net-next, but isn't this reduced overhead coming at the > > > > > > > >>> expense of latency? What if that lower latency is important to the > > > > > > > >>> application and/or consumer? > > > > > > > >> Thats a fair point, but I'd make the counter argument that, as it > > > > > > > >> currently > > > > > > > >> stands, any latency introduced (or removed), is an artifact of our > > > > > > > >> implementation rather than a designed feature of it. That is to say, > > > > > > > >> we make no > > > > > > > >> guarantees at the application level regarding how long it takes to > > > > > > > >> signal data > > > > > > > >> readines from the time we get data off the wire, so I would rather see > > > > > > > >> our > > > > > > > >> throughput raised if we can, as thats been sctp's more pressing > > > > > > > >> achilles heel. > > > > > > > >> > > > > > > > >> > > > > > > > >> Thats not to say I'd like to enable lower latency, but I'd rather have > > > > > > > >> this now, > > > > > > > >> and start pondering how to design that in. Perhaps we can convert the > > > > > > > >> pending > > > > > > > >> flag to a counter to count the number of events we enqueue, and call > > > > > > > >> sk_data_ready every time we reach a sysctl defined threshold. > > > > > > > > > > > > > > > > That and also that there is no chance of the application reading the > > > > > > > > first chunks before all current ToDo's are performed by either the bh > > > > > > > > or backlog handlers for that packet. Socket lock won't be cycled in > > > > > > > > between chunks so the application is going to wait all the processing > > > > > > > > one way or another. > > > > > > > > > > > > > > But it takes time to signal the wakeup to the remote cpu the process > > > > > > > was running on, schedule out the current process on that cpu (if it > > > > > > > has in fact lost it's timeslice), and then finally look at the socket > > > > > > > queue. > > > > > > > > > > > > > > Of course this is all assuming the process was sleeping in the first > > > > > > > place, either in recv or more likely poll. > > > > > > > > > > > > > > I really think signalling early helps performance. > > > > > > > > > > > > > > > > > > > Early, yes, often, not so much :). Perhaps what would be adventageous would be > > > > > > to signal at the start of a set of enqueues, rather than at the end. That would > > > > > > be equivalent in terms of not signaling more than needed, but would eliminate > > > > > > the signaling on every chunk. Perhaps what you could do Marcelo would be to > > > > > > change the sense of the signal_ready flag to be a has_signaled flag. e.g. call > > > > > > sk_data_ready in ulp_event_tail like we used to, but only if the has_signaled > > > > > > flag isn't set, then set the flag, and clear it at the end of the command > > > > > > interpreter. > > > > > > > > > > > > That would be a best of both worlds solution, as long as theres no chance of > > > > > > race with user space reading from the socket before we were done enqueuing (i.e. > > > > > > you have to guarantee that the socket lock stays held, which I think we do). > > > > > > > > > > That is my feeling too. Will work on it. Thanks :-) > > > > > > > > I did the change and tested it on real machines set all for performance. > > > > I couldn't spot any difference between both implementations. > > > > > > > > Set RSS and queue irq affinity for a cpu and taskset netperf and another > > > > app I wrote to run on another cpu. It hits socket backlog quite often > > > > but still do direct processing every now and then. > > > > > > > > With current state, netperf, scenario above. Results of perf sched > > > > record for the CPUs in use, reported by perf sched latency: > > > > > > > > Task | Runtime ms | Switches | Average delay ms | > > > > Maximum delay ms | Maximum delay at | > > > > netserver:3205 | 9999.490 ms | 10 | avg: 0.003 ms | > > > > max: 0.004 ms | max at: 69087.753356 s > > > > > > > > another run > > > > netserver:3483 | 9999.412 ms | 15 | avg: 0.003 ms | > > > > max: 0.004 ms | max at: 69194.749814 s > > > > > > > > With the patch below, same test: > > > > netserver:2643 | 10000.110 ms | 14 | avg: 0.003 ms | > > > > max: 0.004 ms | max at: 172.006315 s > > > > > > > > another run: > > > > netserver:2698 | 10000.049 ms | 15 | avg: 0.003 ms | > > > > max: 0.004 ms | max at: 368.061672 s > > > > > > > > I'll be happy to do more tests if you have any suggestions on how/what > > > > to test. > > > > > > > > ---8<--- > > > > > > > I think this looks reasonable, but can you post it properly please, as a patch > > > against the head of teh net-next tree, rather than a diff from your previous > > > work (which wasn't comitted) > > > > The idea was to not officially post it yet, more just as a reference, > > because I can't see any gains from it. I'm reluctant just due to that, > > no strong opinion here on one way or another. > > > > If you think it's better anyway to signal it early, I'll properly repost > > it. > > > Yeah, your results seem to me to indicate that for your test at least, signaling > early vs. late doesn't make alot of difference, but Dave I think made a point in > principle in that allowing processes to wake up when we start enqueuing can be > better in some situations. So all other things being equal, I'd say go with the > method that you have here. Okay, I'll rebase the patch and post it properly. Thanks Neil! Marcelo -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
