Messages in this thread | | | Date | Fri, 15 Nov 2013 12:56:29 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 10/10] perf record: Add an option to force per-cpu mmaps |
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* Adrian Hunter <adrian.hunter@intel.com> wrote:
> On 15/11/13 13:10, Ingo Molnar wrote: > > > > * Adrian Hunter <adrian.hunter@intel.com> wrote: > > > >>> And I also raised why this shouldn't be the default event tracing > >>> method instead of a weird config option. Per-cpu tracing is cache > >>> compact, it is easier to size properly and in general it is pretty > >>> easy to think about. (It also has less of the TSC timestamp > >>> ordering problems as per thread tracing, at least in theory.) > >>> > >>> Is there something that makes per cpu tracing undesirable as the > >>> default? > >> > >> One reason is to avoid changing the meaning of existing options. > > > > Well, the way the tracing buffers are set up is a mostly tool internal > > matter so in that sense it should be just fine to change the default > > behavior - as long as output remains unchanged (which it should). > > > > Or is there any material change in behavior somewhere? > > Inheritance is enabled automatically with per-cpu mmaps, > although that is one of the reasons people want > per-cpu mmaps.
So, here's the current status quo, there's 4 basic types of profiling that 99% of the people are using, in order of popularity:
perf record <cmd> perf record -a sleep N perf record -p <PID> perf record -t <TID>
The first two (which I'd guess comprise about 95% of real-world usage) have inheritance enabled.
The last two (-p/-t) have inheritance disabled by default.
Correct?
Thanks,
Ingo
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