On Tue, 2010-05-11 at 16:04 +0200, Stephane Eranian wrote: > Hi, > > > I am confused by the inheritance cmd line option of perf record: > > $ perf record -h > usage: perf record [<options>] [<command>] > or: perf record [<options>] -- <command> [<options>] > > -e, --event <event> event selector. use 'perf list' to list > available events > --filter <filter> > event filter > -p, --pid <n> record events on existing process id > -t, --tid <n> record events on existing thread id > -r, --realtime <n> collect data with this RT SCHED_FIFO priority > -R, --raw-samples collect raw sample records from all opened counters > -a, --all-cpus system-wide collection from all CPUs > -A, --append append to the output file to do incremental > profiling > -C, --profile_cpu <n> > CPU to profile on > -f, --force overwrite existing data file (deprecated) > -c, --count event period to sample > -o, --output <file> output file name > -i, --inherit child tasks inherit counters > > This leads to believe that by default inheritance in children is off. > > However, builtin-record.c says: > > static bool inherit = true; > > If that's the case, what's the point of the -i option?
Right, I think we should invert that, does --no-inherit work? > Another side effect of inheritance is that in per-thread mode, > perf creates as many "sessions" as you have CPUs. So > on a 16-way processor, sampling on cycles, perf creates > 16 events and 16 x 2-page sampling buffers. That's a lot of > resources consumed if I am just interested in monitoring > a single-threaded workload. Right, but I think the default of inherit is right, and once you do that you basically have to do the per-task-per-cpu thing, otherwise your fancy 16-way will start spending most of its time in cacheline bounces. That said, !inherit wouldn't need that, so a patch doing that would be nice. ------------------------------------------------------------------------------ _______________________________________________ perfmon2-devel mailing list perfmon2-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/perfmon2-devel
