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

From: Stephane Eranian
Date: Tue Jan 12 2016 - 16:02:14 EST

On Tue, Jan 12, 2016 at 7:48 AM, Arnaldo Carvalho de Melo
<acme@xxxxxxxxxx> 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'.