Messages in this thread | | | Date | Fri, 15 Nov 2013 07:06:43 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 10/10] perf record: Add an option to force per-cpu mmaps |
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* 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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