On Tue, May 11, 2010 at 4:48 PM, Peter Zijlstra <pet...@infradead.org> wrote: > 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. > In that case, don't you think you should also ensure that the buffer is allocated on the NUMA node of the designated per-thread-per-cpu? I don't think it is the case today.
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