linux-kernel - Re: [PATCH v2] perf: disable PERF_RECORD

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Date:	Thu, 17 Oct 2013 17:57:20 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	David Ahern <dsahern@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH v2] perf: disable PERF_RECORD_MMAP2 support

On Thu, Oct 17, 2013 at 5:54 PM, David Ahern <dsahern@...il.com> wrote:
> On 10/17/13 8:28 AM, Stephane Eranian wrote:
>>
>>
>> For now, we disable the extended MMAP record support (MMAP2).
>> We have identified cases where it would not report the correct
>> mapping information, clone(VM_CLONE) but with separate pids.
>> We will revisit the support once we find a solution for this case.
>>
>> The patch changes the kernel to return EINVAL if attr->mmap2
>> is set. The patch also modifies the perf tool to use regular
>> PERF_RECORD_MMAP
>> for synthetic events and it also prevents the tool from requesting
>> attr->mmap2
>> mode because the kernel would reject it.
>>
>> The support will be revisited once the kenrel interface is updated.
>
>
> Why not disable mmap2 as well:
>
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 0ce9febf1ba0..289f34dbe970 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -678,7 +678,7 @@ void perf_evsel__config(struct perf_evsel *evsel,
>         attr->sample_type   |= PERF_SAMPLE_WEIGHT;
>
>     attr->mmap  = track;
> -   attr->mmap2 = track && !perf_missing_features.mmap2;
> +   /* attr->mmap2 = track && !perf_missing_features.mmap2; */
>     attr->comm  = track;
>
It is disabled automatically later on. I checked that. Wanted to minimize
the changes.
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