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

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Message-ID: <87fue0k0gd.fsf@concordia.ellerman.id.au>
Date:   Thu, 13 Jul 2017 22:04:02 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Jin Yao <yao.jin@...ux.intel.com>, 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,
        Jin Yao <yao.jin@...ux.intel.com>
Subject: Re: [PATCH v8 1/7] perf/core: Define the common branch type classification

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