On Fri, May 10, 2013 at 12:18:23PM +0200, Ingo Molnar wrote: > > * Peter Zijlstra <pet...@infradead.org> wrote: > > > > so you mean just detect that by opening events with increasing precise > > > and see how far we could get.. could be I guess, though the 'precise' > > > sysfs attribute seems more fit to me > > > > The other way around, start at ppp end at !p, then use the one that > > worked. > > Really, instead of this silly 'probing until it works' notion, how about > the radical idea that we pass to the kernel our request, and the kernel > fulfills our wish to the best of its ability? > > This could be done as a new PERF_COUNT_HW_CPU_CYCLES_PRECISE event, to > which tooling could migrate, without changing existing semantics. > > The problem with the complex probing is that it's totally unnecessary > complexity that results from lack of passing the right information to the > kernel. Forcing that will only hinder user-space adoption of our precise > profiling facilities.
The part I have trouble with is that its a vague request and you'll get a vague answer. Its very similar to: 'do something' and getting a string of random bytes back. Yes it is 'something', request fulfilled. By doing the probing, userspace knows exactly what it asked and what it'll get. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
