Em Tue, Oct 27, 2015 at 08:15:31AM -0600, David Ahern escreveu: > On 10/27/15 6:33 AM, Arnaldo Carvalho de Melo wrote: > >>Correlating data to user readable information is a key part of perf.
> >Indeed, as best as it can. > >>One option that might be able to solve this problem is to have perf > >>kernel side walk the task list and generate the task events into the > >>ring buffer (task diag code could be leveraged). This would be a lot > > > >It would have to do this over multiple iterations, locklessly wrt the > >task list, in a non-intrusive way, which, in this case, could take > >forever, no? :-) > > taskdiag struggles to keep up because netlink messages have a limited size, > the skb's have to be pushed to userspace and ack'ed and then the walk > proceeds to the next task. > > Filenames for the maps are the biggest killer on throughput wrt kernel side > processing. > > With a multi-MB ring buffer you have a much larger buffer to fill. In > addition perf userspace can be kicked at a low watermark so it is draining > that buffer as fast as it can: > > kernel ---> ring buffer ---> perf --> what? > > The limiter here is perf userspace draining the buffer such that the kernel > side does not have to take much if any break. > > If the "What" is a file (e.g., perf record) then file I/O becomes a limiter. > If the "What" is processing the data (e.g., perf top) we should be able to > come up with some design that at least pulls the data into memory so the > buffer never fills. > > Sure there would need to be some progress limiters put to keep the kernel > side from killing a cpu but I think this kind of design has the best chance > of getting the most information for this class of problem. > > And then for all of the much smaller more typical perf use cases this kind > of data collection is much less expensive than walking proc. taskdiag shows > that and this design is faster and more efficient than taskdiag. Definetely, if we can avoid looking at /proc for what we need, that would be better. Hope you can continue working on that or that someone else picks the baton and get that to a mergeable form. But in extreme cases, not even that would work. - Arnaldo -- To unsubscribe from this list: send the line "unsubscribe linux-perf-users" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
