linux-kernel - Re: [PATCH] perf: disable mmap2 support

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Date:	Thu, 10 Oct 2013 06:56:35 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Arnaldo Carvalho de Melo <acme@...hat.com>
Cc:	Stephane Eranian <eranian@...gle.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, peterz@...radead.org,
	dsahern@...il.com, ak@...ux.intel.com, jolsa@...hat.com,
	hughd@...gle.com, keescook@...omium.org, akpm@...ux-foundation.org
Subject: Re: [PATCH] perf: disable mmap2 support


* Arnaldo Carvalho de Melo <acme@...hat.com> wrote:

> Em Wed, Oct 09, 2013 at 06:17:43PM +0200, Stephane Eranian escreveu:

> > This patch disables the mmap2 record format support for now. The 
> > support needs a bit more work to cover VM_CLONE cases.
> > 
> > The patch leaves attr->mmap2 defined, but returns an error if it is 
> > set. That ensures no PERF_RECORD_MMAP2 record can be generated. Yet it 
> > minimizes the reverts in the perf tool.
> 
> Would be interesting to have a simple new tool that would detect all the 
> mmaps that are shared in a given perf.data file, using the 
> PERF_RECORD_MMAP2 information, and that tool should come together with 
> the reworked kernel ABI, showing how it is used.

Indeed. Let's make that a requirement for the next round of mmap2 patches. 

Issues like this is really why I hate not getting a fully functional 
usecase together with a new ABI - it's _so_ easy to come up with something 
subtly (or not so subtly) incomplete.

> A 'perf test' entry, based on the test programs you guys are using to 
> test this functionality would be even better, showing that all cases 
> you've been striving to cover are in fact covered by the new ABI.

That too, in addition to an actual tool that people can use.

Thanks,

	Ingo
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