linux-kernel - Re: [tip:perf/urgent] perf symbols: Allow lookups by symbol name too

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Date:	Tue, 15 Dec 2009 00:44:06 -0200
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	mingo@...hat.com, hpa@...or.com, paulus@...ba.org,
	linux-kernel@...r.kernel.org, a.p.zijlstra@...llo.nl,
	efault@....de, tglx@...utronix.de, mhiramat@...hat.com,
	mingo@...e.hu, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/urgent] perf symbols: Allow lookups by symbol name too

Em Tue, Dec 15, 2009 at 03:32:30AM +0100, Frederic Weisbecker escreveu:
> On Tue, Dec 15, 2009 at 12:20:20AM -0200, Arnaldo Carvalho de Melo wrote:
> > Em Tue, Dec 15, 2009 at 03:12:03AM +0100, Frederic Weisbecker escreveu:
> > > On Sat, Dec 12, 2009 at 07:22:03AM +0000, tip-bot for Arnaldo Carvalho de Melo wrote:
> > > > Looking over the vmlinux/kallsyms is common enough that I'll add a
> > > > variable to the upcoming struct perf_session to avoid the need to
> > > > use map_groups__find_by_name to get the main vmlinux/kallsyms map.
> > > > 
> > > > The above example looks on the 'variable' symtab, but it is just
> > > > like that for the functions one.
> > > > 
> > > > Also the sort operation is done when we first use
> > > > map__find_symbol_by_name, in a lazy way.
> > > 
> > > It would be nice to also have a kernel symbol resolution
> > > helper independant of any session.
> > > 
> > > The problem is that I need to resolve a kernel variable symbol
> > > very early, when we parse record options. We don't have any
> > > session at this time so I can't retrieve the kmaps.
> > 
> > Humm, I don't think that is a problem, we just have to create the
> > session before processing the args, after all at record time we can use
> > kallsyms already.
> 
> Yeah but we need the output filename before creating it, which
> we even don't have yet at this time.

Well, see top it should shed some light:

        /*
         * FIXME: perf_session__new should allow passing a O_MMAP, so that all this
         * mmap reading, etc is encapsulated in it. Use O_WRONLY for now.
         */
        struct perf_session *session = perf_session__new(NULL, O_WRONLY, false,
                                                         &symbol_conf);

8-)

> May be I should just init it very early without the filename
> and assign it later with a small new helper.
> 
> Another problem is that the record session is not available
> from parse-events.c, may be should I create a single wide scope
> record_session that would be shared among record, top and stat
> so that it's available from parse-event.c
> 
> > > I'm not sure what's the proper way to handle that.
> > 
> > What is the problem? I'm not following :-)
> 
> I think the real problem actually is that I should join
> my bed.
> The above questions will retrieve their trivial essence after
> some sleep :)

Ok, I'm some hours behind you but neverthless ahead of my own bedtime,
lets see tomorrow how to add support for your scenario and for O_MMAP
before some other top-like app needs to use our mutant teenage libperf
kid :-)

- Arnaldo
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