linux-kernel - Re: [PATCH 3/3] perf, x86, lbr: Demand proper privileges for PERF_SAMPLE_BRANCH

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Message-ID: <CABPqkBSCXJN7gLK_e_Q3YVVVFVGS78fo4j2z0+MmriqoXszH+w@mail.gmail.com>
Date:	Thu, 16 May 2013 17:36:11 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Michael Neuling <mikey@...ling.org>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Michael Ellerman <michael@...erman.id.au>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
	Linux PPC dev <linuxppc-dev@...abs.org>
Subject: Re: [PATCH 3/3] perf, x86, lbr: Demand proper privileges for PERF_SAMPLE_BRANCH_KERNEL

On Thu, May 16, 2013 at 1:16 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, May 16, 2013 at 08:15:17PM +1000, Michael Neuling wrote:
>> Peter,
>>
>> BTW PowerPC also has the ability to filter on conditional branches.  Any
>> chance we could add something like the follow to perf also?
>>
>
> I don't see an immediate problem with that except that we on x86 need to
> implement that in the software filter. Stephane do you see any
> fundamental issue with that?
>
On X86, the LBR cannot filter on conditional in HW. Thus as Peter said, it would
have to be done in SW. I did not add that because I think those branches are
not necessarily useful for tools.

>>
>> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
>> index fb104e5..891c769 100644
>> --- a/include/uapi/linux/perf_event.h
>> +++ b/include/uapi/linux/perf_event.h
>> @@ -157,8 +157,9 @@ enum perf_branch_sample_type {
>>       PERF_SAMPLE_BRANCH_ANY_CALL     = 1U << 4, /* any call branch */
>>       PERF_SAMPLE_BRANCH_ANY_RETURN   = 1U << 5, /* any return branch */
>>       PERF_SAMPLE_BRANCH_IND_CALL     = 1U << 6, /* indirect calls */
>> +     PERF_SAMPLE_BRANCH_CONDITIONAL  = 1U << 7, /* conditional branches */
>>
>> -     PERF_SAMPLE_BRANCH_MAX          = 1U << 7, /* non-ABI */
>> +     PERF_SAMPLE_BRANCH_MAX          = 1U << 8, /* non-ABI */
>>  };
>>
>>  #define PERF_SAMPLE_BRANCH_PLM_ALL \
>> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
>> index cdf58ec..5b0b89d 100644
>> --- a/tools/perf/builtin-record.c
>> +++ b/tools/perf/builtin-record.c
>> @@ -676,6 +676,7 @@ static const struct branch_mode branch_modes[] = {
>>       BRANCH_OPT("any_call", PERF_SAMPLE_BRANCH_ANY_CALL),
>>       BRANCH_OPT("any_ret", PERF_SAMPLE_BRANCH_ANY_RETURN),
>>       BRANCH_OPT("ind_call", PERF_SAMPLE_BRANCH_IND_CALL),
>> +     BRANCH_OPT("cnd", PERF_SAMPLE_BRANCH_CONDITIONAL),
>>       BRANCH_END
>>  };
>>
--
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