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

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Message-ID: <CABPqkBRz42juzqHqGY8uaBw5kwoCp6_f99k-Gu+nK3kZ5tR7DA@mail.gmail.com>
Date:	Tue, 12 Jan 2016 13:02:05 -0800
From:	Stephane Eranian <eranian@...gle.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	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 7:48 AM, Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
> Em Tue, Jan 12, 2016 at 04:34:40PM +0100, Peter Zijlstra escreveu:
>> 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.
>
> How will we collect the mtime for the DSOs in PERF_RECORD_MMAP records
> if we don't look at those records? What mtime are you talking about?
>
I think the post-processing of MMAP could be sped up if they were
saved out-of-band
inside of with the samples. Isn't that what the auxbuffer allows you to do?

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