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From: Stephane Eranian on 11 May 2010 10:10
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?

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.

Am I missing something here?
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Prev: [OOPS] apbuart.c: Two problems related to grlib_apbuart_configure()
Next: [PATCHv5 0/3] Introduce the /proc/socinfo and use it to export OMAP data