On Fri, Sep 01, 2017 at 01:21:03AM -0700, Stephane Eranian wrote: SNIP
> >> 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 > > > It is not just a matter of modifier, you need to have the kernel > record just what you want. > AFAIK, the only way for the the kernel to record timings on sampling events > is to force PERF_SAMPLE_READ. So the T modifier would have to also set > that format, > at which point, I wonder how useful it is compared to S. well :S is meant to be used for leader sampling, so in addition to what you described it also disables sampling on all other group members, which I don't think you want > > Alternatively, we could improve the kernel to support recording timing with > PERF_SAMPLE_TIMINGS as a pair of u64 to represent time_enabled, time_running. > That would avoid the whole PERF_SAMPLE_READ and the extra u64 it records. > Recording the value of the sampling event is not very useful because > it keeps being > reset for each period. sounds good.. or if we mind taking another bit out of the sample_type for this we could have new read_format bit PERF_FORMAT_NO_COUNT, which would omit the count values jirka
