Date: Wed, 15 Feb 2012 11:47:33 -0200
From: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Luigi Semenzato <semenzato@chromium.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Paul Mackerras <paulus@samba.org>, Ingo Molnar <mingo@elte.hu>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vasiliy Kulikov <segoon@openwall.com>,
        Stephen Wilson <wilsons@start.ca>, Oleg Nesterov <oleg@redhat.com>,
        Tejun Heo <tj@kernel.org>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        Andi Kleen <ak@linux.intel.com>,
        Lucas De Marchi <lucas.demarchi@profusion.mobi>,
        Greg Kroah-Hartman <gregkh@suse.de>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        "Rafael J. Wysocki" <rjw@sisk.pl>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        David Ahern <dsahern@gmail.com>, Namhyung Kim <namhyung@gmail.com>,
        Robert Richter <robert.richter@amd.com>, linux-kernel@vger.kernel.org,
        sonnyrao@chromium.org, olofj@chromium.org, eranian@google.com
Subject: Re: [PATCH] Perf: bug fix: distinguish between rename and exec
Message-ID: <20120215134733.GL28614@infradead.org>
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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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