linux-kernel - Re: [RFC V1 11/11] perf: Capture branch privilege information

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Date:   Wed, 2 Feb 2022 16:41:03 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     James Clark <james.clark@....com>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-perf-users@...r.kernel.org, Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [RFC V1 11/11] perf: Capture branch privilege information



On 1/25/22 9:09 PM, James Clark wrote:
> 
> 
> On 24/01/2022 04:30, Anshuman Khandual wrote:
>> Platforms like arm64 could capture privilege level information for all the
>> branch records. Hence this adds a new element in the struct branch_entry to
>> record the privilege level information, which could be requested through a
>> new event.attr.branch_sample_type flag PERF_SAMPLE_BRANCH_PRIV_SAVE. While
>> here, update the BRBE driver as required.
>>
>> Cc: Will Deacon <will@...nel.org>
>> Cc: Mark Rutland <mark.rutland@....com>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
>> Cc: Jiri Olsa <jolsa@...hat.com>
>> Cc: Namhyung Kim <namhyung@...nel.org>
>> Cc: linux-arm-kernel@...ts.infradead.org
>> Cc: linux-perf-users@...r.kernel.org
>> Cc: linux-kernel@...r.kernel.org
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>> ---
>>  drivers/perf/arm_pmu_brbe.c              | 28 ++++++++++++++++++++++++
>>  include/linux/perf_event.h               |  5 +++++
>>  include/uapi/linux/perf_event.h          | 13 ++++++++++-
>>  tools/include/uapi/linux/perf_event.h    | 13 ++++++++++-
>>  tools/perf/Documentation/perf-record.txt |  1 +
>>  tools/perf/util/parse-branch-options.c   |  1 +
>>  6 files changed, 59 insertions(+), 2 deletions(-)
>>
> [...]
>> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
>> index 361fdc6b87a0..4d77710f7a4e 100644
>> --- a/include/uapi/linux/perf_event.h
>> +++ b/include/uapi/linux/perf_event.h
>> @@ -204,6 +204,8 @@ enum perf_branch_sample_type_shift {
>>  
>>  	PERF_SAMPLE_BRANCH_HW_INDEX_SHIFT	= 17, /* save low level index of raw branch records */
>>  
>> +	PERF_SAMPLE_BRANCH_PRIV_SAVE_SHIFT	= 18, /* save privillege mode */
> 
> privillege -> privilege

Fixed.

> 
>> +
>>  	PERF_SAMPLE_BRANCH_MAX_SHIFT		/* non-ABI */
>>  };
>>  
>> @@ -233,6 +235,8 @@ enum perf_branch_sample_type {
>>  
>>  	PERF_SAMPLE_BRANCH_HW_INDEX	= 1U << PERF_SAMPLE_BRANCH_HW_INDEX_SHIFT,
>>  
>> +	PERF_SAMPLE_BRANCH_PRIV_SAVE	= 1U << PERF_SAMPLE_BRANCH_PRIV_SAVE_SHIFT,
>> +
> 
> Can you also add the new entry to the perf verbose printer otherwise it looks like
> it's not being set on branch_sample_type
> (as in when using ./perf record -j any_call,u,priv -vvv):

Sure, will do.

> 
> 	static void __p_branch_sample_type(char *buf, size_t size, u64 value)
> 	{
> 	#define bit_name(n) { PERF_SAMPLE_BRANCH_##n, #n }
> 		struct bit_names bits[] = {
> 			bit_name(USER), bit_name(KERNEL), bit_name(HV), bit_name(ANY),
> 			bit_name(ANY_CALL), bit_name(ANY_RETURN), bit_name(IND_CALL),
> 			bit_name(ABORT_TX), bit_name(IN_TX), bit_name(NO_TX),
> 			bit_name(COND), bit_name(CALL_STACK), bit_name(IND_JUMP),
> 			bit_name(CALL), bit_name(NO_FLAGS), bit_name(NO_CYCLES),
> 			bit_name(HW_INDEX),
> 			{ .name = NULL, }
> 		};
> 	#undef bit_name
> 		__p_bits(buf, size, value, bits);
> 	}
> 
> PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT is also missing so it probably makes sense to add it
> at the same time as that was expanded for BRBE.

Posted a patch for PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT here but will update
for the new 'priv' request via this series.

https://lore.kernel.org/all/1643799443-15109-1-git-send-email-anshuman.khandual@arm.com/