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

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Date:	Fri, 15 Nov 2013 14:52:44 +0200
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	linux-kernel@...r.kernel.org, David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...hat.com>,
	Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH 10/10] perf record: Add an option to force per-cpu mmaps

On 15/11/13 14:03, Peter Zijlstra wrote:
> On Fri, Nov 15, 2013 at 12:56:29PM +0100, Ingo Molnar wrote:
>> 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.
> 
> Yes, and I would expect it to be disabled for the TID option as you
> explicitly select a single threads.

So you want -t to imply -i ?

That means if you want inheritance you have to do

	-t <TID> --no-no-inherit

Or do you want another option --inherit

> 
> For the process wide thing it would make sense to enable inheritance by
> default though.
> 
> So the big trade-off is that for single threaded processes which do not
> fork you now have a single buffer, whereas with the inheritance option
> you'll end up with nr_cpus buffers by default.
> 
> I suppose for most normal people that's not really an issue; and I
> suppose all people with silly large machines already pay extra attention
> -- but at least make it explicit and very clear that this is so.
> 
> 
> 
> 

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