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Date:   Thu, 6 Apr 2017 08:09:06 +0800
From:   "Jin, Yao" <yao.jin@...ux.intel.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jiri Olsa <jolsa@...nel.org>, linux-kernel@...r.kernel.org,
        ak@...ux.intel.com, kan.liang@...el.com, yao.jin@...el.com,
        Peter Zijlstra <peterz@...radead.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v1 1/5] perf/core: Define the common branch type
 classification



On 4/5/2017 12:09 AM, Arnaldo Carvalho de Melo wrote:
> Em Tue, Apr 04, 2017 at 11:52:53PM +0800, Jin, Yao escreveu:
>>
>> On 4/4/2017 10:18 PM, Arnaldo Carvalho de Melo wrote:
>>> Adding the perf kernel maintainers to the CC list.
>>>
>>> Em Fri, Mar 31, 2017 at 11:18:38PM +0800, Jin Yao escreveu:
>>>> 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 branch type. The branch type is defined in lbr.c.
>>>>
>>>> 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.
>>>>
>>>> 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.
>>>>
>>>> Signed-off-by: Jin Yao <yao.jin@...ux.intel.com>
>>>> ---
>>>>    include/uapi/linux/perf_event.h       | 24 +++++++++++++++++++++++-
>>>>    tools/include/uapi/linux/perf_event.h | 24 +++++++++++++++++++++++-
>>>>    2 files changed, 46 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
>>>> index d09a9cd..4d731fd 100644
>>>> --- a/include/uapi/linux/perf_event.h
>>>> +++ b/include/uapi/linux/perf_event.h
>>>> @@ -174,6 +174,8 @@ enum perf_branch_sample_type_shift {
>>>>    	PERF_SAMPLE_BRANCH_NO_FLAGS_SHIFT	= 14, /* no flags */
>>>>    	PERF_SAMPLE_BRANCH_NO_CYCLES_SHIFT	= 15, /* no cycles */
>>>> +	PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT	= 16, /* save branch type */
>>>> +
>>>>    	PERF_SAMPLE_BRANCH_MAX_SHIFT		/* non-ABI */
>>>>    };
>>>> @@ -198,9 +200,27 @@ enum perf_branch_sample_type {
>>>>    	PERF_SAMPLE_BRANCH_NO_FLAGS	= 1U << PERF_SAMPLE_BRANCH_NO_FLAGS_SHIFT,
>>>>    	PERF_SAMPLE_BRANCH_NO_CYCLES	= 1U << PERF_SAMPLE_BRANCH_NO_CYCLES_SHIFT,
>>>> +	PERF_SAMPLE_BRANCH_TYPE_SAVE	=
>>>> +		1U << PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT,
>>>> +
>>>>    	PERF_SAMPLE_BRANCH_MAX		= 1U << PERF_SAMPLE_BRANCH_MAX_SHIFT,
>>>>    };
>>>> +/*
>>>> + * Common flow change classification
>>>> + */
>>>> +enum {
>>>> +	PERF_BR_NONE		= 0,		/* unknown */
>>>> +	PERF_BR_JCC_FWD		= 1 << 1,	/* conditional forward jump */
>>>> +	PERF_BR_JCC_BWD		= 1 << 2,	/* conditional backward jump */
>>>> +	PERF_BR_JMP		= 1 << 3,	/* jump */
>>>> +	PERF_BR_IND_JMP		= 1 << 4,	/* indirect jump */
>>>> +	PERF_BR_CALL		= 1 << 5,	/* call */
>>>> +	PERF_BR_IND_CALL	= 1 << 6,	/* indirect call */
>>>> +	PERF_BR_RET		= 1 << 7,	/* return */
>>>> +	PERF_BR_FAR_BRANCH	= 1 << 8,	/* SYSCALL,SYSRET,IRQ,... */
>>> Humm, wouldn't be better to have those in separate buckets? I.e.
>>>
>>>     PERF_BR_SYSCALL
>>>     PERF_BR_SYSRET,
>>>     PERF_BR_IRQ
>>>
>>> etc?
>> There are also other types. I.e. abort, ..... I use FAR_BRANCH is because I
>> just want to differentiate between basic branch types and others. (others
>> may be too much and platform specific).
> I understand that this is what you need right now, but "syscall",
> "sysret", "irq", look generic enough, no?
>
> Really, really arch specific stuff could indeed be lumped together in a
> FAR_BRANCH, but those used as an example, above (/*
> SYSCALL,SYSRET,IRQ,... */) seems potentially useful to have untangled?

After considerations, yes, you are right. I will fix this in v2.

Thanks
Jin Yao

>>> And why a bitmask? /me reads a bit more...  couldn't find a reason for
>>> this:
>>>
>>> +             type:9,     /* branch type */
>>>
>>> Do you have a reason to use 9 bits? Why not just:
>>>
>>> enum {
>>> 	PERF_BR_NONE		= 0,	/* unknown */
>>> 	PERF_BR_JCC_FWD		= 1,	/* conditional forward jump */
>>> 	PERF_BR_JCC_BWD		= 2,	/* conditional backward jump */
>>> 	PERF_BR_JMP		= 3,	/* jump */
>>> 	PERF_BR_IND_JMP		= 4,	/* indirect jump */
>>> 	PERF_BR_CALL		= 5,	/* call */
>>> 	PERF_BR_IND_CALL	= 6,	/* indirect call */
>>> 	PERF_BR_RET		= 7,	/* return */
>>> 	PERF_BR_FAR_BRANCH	= 8,	/* SYSCALL,SYSRET,IRQ,... */
>>>
>>> And then use, say, 4 or 5 bits for that type field?
>>>
>>> I must be missing something trivial ;-\
>>>
>>> - Arnaldo
>> You are right. I made things more complicated. Yes, the definitions should
>> be clear and simple. I will redefine them in v2.
> Thanks, I wasn't missing anything, uff :-)
>   
>> Thanks
>> Jin Yao
>>
>>>> +};
>>>> +
>>>>    #define PERF_SAMPLE_BRANCH_PLM_ALL \
>>>>    	(PERF_SAMPLE_BRANCH_USER|\
>>>>    	 PERF_SAMPLE_BRANCH_KERNEL|\
>>>> @@ -999,6 +1019,7 @@ union perf_mem_data_src {
>>>>     *     in_tx: running in a hardware transaction
>>>>     *     abort: aborting a hardware transaction
>>>>     *    cycles: cycles from last branch (or 0 if not supported)
>>>> + *      type: branch type
>>>>     */
>>>>    struct perf_branch_entry {
>>>>    	__u64	from;
>>>> @@ -1008,7 +1029,8 @@ struct perf_branch_entry {
>>>>    		in_tx:1,    /* in transaction */
>>>>    		abort:1,    /* transaction abort */
>>>>    		cycles:16,  /* cycle count to last branch */
>>>> -		reserved:44;
>>>> +		type:9,     /* branch type */
>>>> +		reserved:35;
>>>>    };
>>>>    #endif /* _UAPI_LINUX_PERF_EVENT_H */
>>>> diff --git a/tools/include/uapi/linux/perf_event.h b/tools/include/uapi/linux/perf_event.h
>>>> index d09a9cd..4d731fd 100644
>>>> --- a/tools/include/uapi/linux/perf_event.h
>>>> +++ b/tools/include/uapi/linux/perf_event.h
>>>> @@ -174,6 +174,8 @@ enum perf_branch_sample_type_shift {
>>>>    	PERF_SAMPLE_BRANCH_NO_FLAGS_SHIFT	= 14, /* no flags */
>>>>    	PERF_SAMPLE_BRANCH_NO_CYCLES_SHIFT	= 15, /* no cycles */
>>>> +	PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT	= 16, /* save branch type */
>>>> +
>>>>    	PERF_SAMPLE_BRANCH_MAX_SHIFT		/* non-ABI */
>>>>    };
>>>> @@ -198,9 +200,27 @@ enum perf_branch_sample_type {
>>>>    	PERF_SAMPLE_BRANCH_NO_FLAGS	= 1U << PERF_SAMPLE_BRANCH_NO_FLAGS_SHIFT,
>>>>    	PERF_SAMPLE_BRANCH_NO_CYCLES	= 1U << PERF_SAMPLE_BRANCH_NO_CYCLES_SHIFT,
>>>> +	PERF_SAMPLE_BRANCH_TYPE_SAVE	=
>>>> +		1U << PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT,
>>>> +
>>>>    	PERF_SAMPLE_BRANCH_MAX		= 1U << PERF_SAMPLE_BRANCH_MAX_SHIFT,
>>>>    };
>>>> +/*
>>>> + * Common flow change classification
>>>> + */
>>>> +enum {
>>>> +	PERF_BR_NONE		= 0,		/* unknown */
>>>> +	PERF_BR_JCC_FWD		= 1 << 1,	/* conditional forward jump */
>>>> +	PERF_BR_JCC_BWD		= 1 << 2,	/* conditional backward jump */
>>>> +	PERF_BR_JMP		= 1 << 3,	/* jump */
>>>> +	PERF_BR_IND_JMP		= 1 << 4,	/* indirect jump */
>>>> +	PERF_BR_CALL		= 1 << 5,	/* call */
>>>> +	PERF_BR_IND_CALL	= 1 << 6,	/* indirect call */
>>>> +	PERF_BR_RET		= 1 << 7,	/* return */
>>>> +	PERF_BR_FAR_BRANCH	= 1 << 8,	/* SYSCALL,SYSRET,IRQ,... */
>>>> +};
>>>> +
>>>>    #define PERF_SAMPLE_BRANCH_PLM_ALL \
>>>>    	(PERF_SAMPLE_BRANCH_USER|\
>>>>    	 PERF_SAMPLE_BRANCH_KERNEL|\
>>>> @@ -999,6 +1019,7 @@ union perf_mem_data_src {
>>>>     *     in_tx: running in a hardware transaction
>>>>     *     abort: aborting a hardware transaction
>>>>     *    cycles: cycles from last branch (or 0 if not supported)
>>>> + *      type: branch type
>>>>     */
>>>>    struct perf_branch_entry {
>>>>    	__u64	from;
>>>> @@ -1008,7 +1029,8 @@ struct perf_branch_entry {
>>>>    		in_tx:1,    /* in transaction */
>>>>    		abort:1,    /* transaction abort */
>>>>    		cycles:16,  /* cycle count to last branch */
>>>> -		reserved:44;
>>>> +		type:9,     /* branch type */
>>>> +		reserved:35;
>>>>    };
>>>>    #endif /* _UAPI_LINUX_PERF_EVENT_H */
>>>> -- 
>>>> 2.7.4

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