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SubjectRe: [PATCH 10/10] perf record: Add an option to force per-cpu mmaps

* Arnaldo Carvalho de Melo <acme@infradead.org> wrote:

> +--force-per-cpu::
> + Force the use of per-cpu mmaps. By default, when tasks are specified (i.e. -p,
> + -t or -u options) per-thread mmaps are created. This option overrides that and
> + forces per-cpu mmaps. A side-effect of that is that inheritance is
> + automatically enabled. Add the -i option also to disable inheritance.

So I still haven't seen an explanation why it's called 'force'
anything. AFAICS nothing is 'forced' really, this is simply another
trace-ringbuffer setup method, right?

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?

Thanks,

Ingo


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