On Fri, Nov 10, 2017 at 11:14:51AM +0000, Bruce Richardson wrote: > On Fri, Nov 10, 2017 at 11:42:56AM +0100, Daniel Bristot de Oliveira wrote: > > > > > > On 11/10/2017 11:14 AM, Ananyev, Konstantin wrote: > > > Agree with Adrian here - the patch doesn't fix the problem in any case, > > > > I would agree with you if it were possible to assume one can fully > > isolate a CPU on Linux... but it is not... > > > > This: > > https://lwn.net/Articles/659490/ > > > > is still an open issue, and the reason why it is an open issue is the > > kernel threads that need to run on every CPU, mainly when using the > > PREEMPT_RT, which turns almost everything on threads. > > > > > while introducing an unnecessary slowdown in testpmd iofwd mode. > > > Please think up some other approach. > > > > The other approach is to increase the priority of all other threads that > > run on the isolate CPU. But that is not a good idea at all, as the other > > threads might preempt the busy-loop thread at the worst possible moment. > > > > Using the knowledge of the thread about when it is the best time to give > > a chance for other threads to run would be a smarter decision. > > > I don't like having this in the main loop either, and to echo others I > wouldn't have thought that testpmd was actually used as anything other > than a testing app. Also, I would have thought that running it at > realtime priority wouldn't be a good idea, because of exactly this > problem.
Bruce, Its just as an example for application developers, in the official DPDK repository. And its disabled by default so it does not affect the performance numbers. That said, you have a problem integrating the patch? > On the specifics of the solution, would using sched_yield() rather than > nanosleep not be more suitable, given that the reason for this sleep is > just to give the CPU to other threads? > > /Bruce Yes but unfortunately "sched_yield()" does not return in a timely fashion, we would need a new "sched_yield_time(X us)" with a guaranteed return from the call in a maximum of X us. (Note the values of nanosleep_frequency=100Hz, nanosleep_length=10us, does increase the latency values a bit but still maintains acceptable latency). The arguments about performance must be considered against this results. Yes Bruce sched_yield() would be mkore
