linux-kernel - Re: perf: prctl(PR_TASK_PERF_EVENTS

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Message-ID: <1327931107.2446.205.camel@twins>
Date:	Mon, 30 Jan 2012 14:45:07 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Frédéric Weisbecker <fweisbec@...il.com>,
	Andrew Steets <asteets@...advisors.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: perf: prctl(PR_TASK_PERF_EVENTS_DISABLE) has no effect

On Mon, 2012-01-30 at 12:31 +0100, Ingo Molnar wrote:
> * Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> 
> > On Mon, 2012-01-30 at 11:11 +0100, Ingo Molnar wrote:
> > > So, what workflow are you suggesting to Andrew?
> > 
> > Librarize perf record, then in your code do something like:
> > 
> > #include "perf_record.h"
> 
> Maybe. (and then it shouldnt be limited to perf_record.h but 
> should be events.h plus libevents.so or such)

Yes it should be, you want to reserve the more generic name for less
narrow interfaces.

> > 
> >   handle = perf_record_init(); /* creates perf events and creates
> >                                   a record thread that writes samples
> >                                   to perf.data, consumes env(PERF_*)
> >                                   for configuration, registers with
> >                                   at_exit() for cleanup */
> >   if (!handle)
> >     /* burn */
> > 
> >   /* do you other code */
> > 
> >   perf_record_start(handle);
> > 
> >   /* do the bit you want profiled */
> > 
> >   perf_record_stop(handle);
> > 
> > Then build with -lperfrecord or so. Not too hard, right?
> 
> Isnt a simple prctl() so much easier and faster?

I really don't want to add another two prctl()s for this, ideally I'd
remove the ones we have now, but I've never done due to maintaining
backwards blah..

> What's your concern with the prctl()? This would arguably be the 
> right kind of usage for prctl(): it's an established API/ABI for 
> process/task-wide settings.

Its doing things backwards, also the whole concept of allowing people to
hide things from a profiler is so rotten I'm not willing to even
consider the notion.
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