linux-kernel - Re: [RFC] perf record: missing buildid for callstack modules

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Message-ID: <20160112153440.GJ6357@twins.programming.kicks-ass.net>
Date:	Tue, 12 Jan 2016 16:34:40 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Stephane Eranian <eranian@...gle.com>,
	Namhyung Kim <namhyung@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jiri Olsa <jolsa@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: Re: [RFC] perf record: missing buildid for callstack modules

On Tue, Jan 12, 2016 at 11:38:05AM -0300, Arnaldo Carvalho de Melo wrote:
> > Also, just parsing the gigabytes of data that comes out of perf-record
> > takes significant time, let alone poking around the filesystem and
> 
> Right, that is what we would elliminate with stashing the content-based
> cookie into a PERF_RECORD_MMAP3 record.

Again, how would you go about getting that cookie for a DSO? The whole
kernel isn't involved with dlopen(), all it sees is a mmap(PROT_EXEC).

> BTW, mtime would incur in postprocessing it all.

mtime can still warn you if things are non-matching at report time
without this post-processing, and thereby solves the problem of staring
at broken/wrong data.

It doesn't get you right data, but knowing your data is broken allows
you to manually do things 'right'.