On Fri, Dec 19, 2014 at 08:48:07AM -0800, Andy Lutomirski wrote: > On Fri, Dec 19, 2014 at 3:23 AM, Peter Zijlstra <pet...@infradead.org> wrote: > > On Thu, Dec 18, 2014 at 04:22:59PM -0800, Andy Lutomirski wrote: > >> Bad news: this patch is incorrect, I think. Take a look at > >> update_rq_clock -- it does fancy things involving irq time and > >> paravirt steal time. So this patch could result in extremely > >> non-monotonic results. > > > > Yeah, I'm not sure how (and if) we could make all that work :/ > > I obviously can't comment on what Facebook needs, but if I were > rigging something up to profile my own code*, I'd want a count of > elapsed time, including user, system, and probably interrupt as well. > I would probably not want to count time during which I'm not > scheduled, and I would also probably not want to count steal time. > The latter makes any implementation kind of nasty. > > The API presumably doesn't need to be any particular clock id for > clock_gettime, and it may not even need to be clock_gettime at all. > > Is perf self-monitoring good enough for this? If not, can we make it > good enough?
Yeah, I think you should be able to use that. You could count a NOP event and simply use its activated time. We have PERF_COUNT_SW_DUMMY for such purposes iirc. The advantage of using perf self profiling is that it (obviously) extends to more than just walltime. -- 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/
