linux-kernel - Re: [PATCH] Perf: bug fix: distinguish between rename and exec

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Date:	Wed, 15 Feb 2012 11:47:33 -0200
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Luigi Semenzato <semenzato@...omium.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Stephen Wilson <wilsons@...rt.ca>,
	Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	David Ahern <dsahern@...il.com>,
	Namhyung Kim <namhyung@...il.com>,
	Robert Richter <robert.richter@....com>,
	linux-kernel@...r.kernel.org, sonnyrao@...omium.org,
	olofj@...omium.org, eranian@...gle.com
Subject: Re: [PATCH] Perf: bug fix: distinguish between rename and exec

Em Wed, Feb 15, 2012 at 01:48:33PM +0100, Peter Zijlstra escreveu:
> I really dislike changing generic code purely for the purpose of
> instrumentation like this. Better to pull perf_event_comm() out of here
> if you want to change semantics.
> 
> Personally I couldn't care less about renames, I think they're a waste
> of time, so I'm ok with the simple patch moving the perf_event_comm()
> into setup_new_exec() and possibly renaming it to perf_event_exec().
> 
> Acme, do you care about renames?

I like your idea of keeping the semantics of PERF_RECORD_COMM and
introducing a PERF_RECORD_EXEC, just have to think about how to handle
that in a way that the tools detect that we have PERF_RECORD_EXEC...

Humm, will be yet another fallback for setting an perf_event_attr bit,
just like with .sample_id_all and .exclude_{guest,host}...

That together with the per class errnos + __strerror() method will allow
to move all the event creation finally to perf_evlist__open() where all
this gets nicely hidden away from poor tools.

We can then even have an ui__evlist_perror() method that does all the
ui__warning calls, etc.

So, yes, from a tooling perspective, I want to be notified of renames
and being able to stop relying on PERF_RECORD_COMM to call
map_groups__flush and instead do it at PERF_RECORD_EXEC seems a
bonus.

- Arnaldo
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