On Wed, Aug 30, 2017 at 11:21:23PM -0700, Stephane Eranian wrote: > Hi, > > > On Mon, Aug 28, 2017 at 1:41 PM, Andi Kleen <a...@firstfloor.org> wrote: > >> So I think we are good to go. to capture multiplexing scaling factor > >> when sampling simply use the S > >> modifier. > >> But to my surprise, newer kernels are not happy with the cmdline: > >> $ perf record -e cycles:S noploop 1 > >> Error: > >> The sys_perf_event_open() syscall returned with 22 (Invalid argument) > >> for event (cycles:Su). > >> /bin/dmesg may provide additional information. > >> No CONFIG_PERF_EVENTS=y kernel support configured? > > > > Likely due to > > > > ba5213ae6b88 perf/core: Correct event creation with PERF_FORMAT_GROUP > > > > It's not supported with inherited events. > > > Yes, and other things have changed as well. I did a bit of research to > figure out how > to make this work out-of the-box with the latest perf (v4.13). It > turns out you need to > combine multiple options and an event modifier. This is quite cumbersome > but here it is: > > $ perf record --no-inherit --running-time -e cycles:S ........ > > You need: > - no-inherit: the kernel does not know how to deal with multiplexing > when events are inherited > - running-time: this used to be automatic for PERF_SAMPLE_READ with > perf record, now it is not > This includes TIME_ENABLED/TIME_RUNNING in the sample_read format. > - :S : to add a PERF_SAMPLE_READ to each sample, it encapsulates the > event value + timings. > We do not care about the value but are only interested in the timings. > > The kernel cannot record the timings without a PERF_SAMPLE_READ. > > I am also surprised to see that perf record keep inherit=1 in > system-wide mode. I don't think this > is relavant in this mode. But the kernel this fails in this case, > which I think is a bug. In system-wide > mode, the attr-.no_inherit should be ignored. We can fix perf record > to avoid this in system-wide. > > The cmdline above works for both per-thread and system-wide modes. > > So I think we do not need my patch or variations thereof, everything > is there, though a bit difficult > to combine.
hum, how about we introduce new modifier to attach timing info, like: $ perf record -e cycles:T .... modifiers might be scares resource, but we don't add them every day, and this requirement looks generic jirka
