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? * I do this today using CLOCK_MONOTONIC --Andy -- Andy Lutomirski AMA Capital Management, LLC -- 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/
