On 15/11/13 14:05, Ingo Molnar wrote: > > * Peter Zijlstra <pet...@infradead.org> wrote: > >> On Fri, Nov 15, 2013 at 12:56:29PM +0100, Ingo Molnar wrote: >>> So, here's the current status quo, there's 4 basic types of profiling >>> that 99% of the people are using, in order of popularity: >>> >>> perf record <cmd> >>> perf record -a sleep N >>> perf record -p <PID> >>> perf record -t <TID> >>> >>> The first two (which I'd guess comprise about 95% of real-world usage) >>> have inheritance enabled. >>> >>> The last two (-p/-t) have inheritance disabled by default. >> >> Yes, and I would expect it to be disabled for the TID option as you >> explicitly select a single threads. > > Correct. > >> For the process wide thing it would make sense to enable inheritance >> by default though. >> >> So the big trade-off is that for single threaded processes which do >> not fork you now have a single buffer, whereas with the inheritance >> option you'll end up with nr_cpus buffers by default. >> >> I suppose for most normal people that's not really an issue; and I >> suppose all people with silly large machines already pay extra >> attention -- but at least make it explicit and very clear that this >> is so. > > Do the first variant, 'perf record <cmd>', already use per CPU > buffers?
Yes. Another difference (and I need to fix the patch) is that per-cpu mmaps require PERF_SAMPLE_TIME so that the events do not appear out of order. -- 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/
