linux-kernel - Re: [PATCH v8 1/7] perf/core: Define the common branch type classification

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Date:   Thu, 13 Jul 2017 20:33:13 +0800
From:   "Jin, Yao" <yao.jin@...ux.intel.com>
To:     Michael Ellerman <mpe@...erman.id.au>, acme@...nel.org,
        jolsa@...nel.org, peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com
Cc:     Linux-kernel@...r.kernel.org, ak@...ux.intel.com,
        kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH v8 1/7] perf/core: Define the common branch type
 classification

Sure, thanks so much!


On 7/13/2017 8:04 PM, Michael Ellerman wrote:
> Jin Yao <yao.jin@...ux.intel.com> writes:
>
>> It is often useful to know the branch types while analyzing branch
>> data. For example, a call is very different from a conditional branch.
>>
>> Currently we have to look it up in binary while the binary may later
>> not be available and even the binary is available but user has to take
>> some time. It is very useful for user to check it directly in perf
>> report.
>>
>> Perf already has support for disassembling the branch instruction
>> to get the x86 branch type.
>>
>> To keep consistent on kernel and userspace and make the classification
>> more common, the patch adds the common branch type classification
>> in perf_event.h.
>>
>> The patch only defines a minimum but most common set of branch types.
>>
>> PERF_BR_UNKNOWN         : unknown
>> PERF_BR_COND            ：conditional
>> PERF_BR_UNCOND          : unconditional
>> PERF_BR_IND             : indirect
>> PERF_BR_CALL            : function call
>> PERF_BR_IND_CALL        : indirect function call
>> PERF_BR_RET             : function return
>> PERF_BR_SYSCALL         : syscall
>> PERF_BR_SYSRET          : syscall return
>> PERF_BR_COND_CALL       : conditional function call
>> PERF_BR_COND_RET        : conditional function return
>>
>> The patch also adds a new field type (4 bits) in perf_branch_entry
>> to record the branch type.
>>
>> Since the disassembling of branch instruction needs some overhead,
>> a new PERF_SAMPLE_BRANCH_TYPE_SAVE is introduced to indicate if it
>> needs to disassemble the branch instruction and record the branch
>> type.
> Acked-by: Michael Ellerman <mpe@...erman.id.au> (powerpc)
>
> If you like.
>
> cheers