linux-kernel - Re: [PATCH v6 1/7] perf/core: Define the common branch type classification

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Date:   Tue, 11 Jul 2017 11:00:55 +0800
From:   "Jin, Yao" <yao.jin@...ux.intel.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Peter Zijlstra <peterz@...radead.org>,
        Segher Boessenkool <segher@...nel.crashing.org>
Cc:     acme@...nel.org, jolsa@...nel.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, kan.liang@...el.com,
        ak@...ux.intel.com, linuxppc-dev@...ts.ozlabs.org,
        Linux-kernel@...r.kernel.org, yao.jin@...el.com
Subject: Re: [PATCH v6 1/7] perf/core: Define the common branch type
 classification



On 7/11/2017 10:28 AM, Michael Ellerman wrote:
> "Jin, Yao" <yao.jin@...ux.intel.com> writes:
>
>> On 7/10/2017 9:46 PM, Peter Zijlstra wrote:
>>> On Mon, Jul 10, 2017 at 08:10:50AM -0500, Segher Boessenkool wrote:
>>>
>>>>> PERF_BR_INT is triggered by instruction "int" .
>>>>> PERF_BR_IRQ is triggered by interrupts, traps, faults (the ring 0,3
>>>>> transition).
>>>> So your "PERF_BR_INT" is a system call?
>>> The "INT" thing has indeed been used as system call mechanism (typically
>>> INT 80). But these days we have special purpose syscall instructions.
>>>
>>> It could maybe be compared to the PPC "Unconditional TRAP with
>>> immediate" where you use the immediate value as an index into a handler
>>> vector.
>>>
>>>> And PERF_BR_IRQ is not an interrupt request (as its name suggests),
>>>> not what we call an "external interrupt" either; instead it is every
>>>> interrupt that is not a system call?
>>> It is actual interrupts, but also faults, traps and all the other
>>> exceptions not caused by "INT" I think.
>>>
>> Yes. It's interrupt, traps, faults. If from is in the user space and to
>> is in the kernel, it indicates the ring3 -> ring0 transition.
>>
>> If the from instruction is not syscall or other ring transition
>> instruction, it should be interrupt, traps and faults. That's how we get
>> the PERF_BR_IRQ on x86.
>>
>> Anyway, maybe we just use a minimum but the most common set of branch
>> types now, it could be a good start and acceptable on all architectures.
>>
>> PERF_BR_COND        = 1,    /* conditional */
>> PERF_BR_UNCOND        = 2,    /* unconditional */
>> PERF_BR_IND        = 3,    /* indirect */
>> PERF_BR_CALL        = 4,    /* call */
>> PERF_BR_IND_CALL    = 5,    /* indirect call */
>> PERF_BR_RET        = 6,    /* return */
> That would be fine by me, if you're sick of talking about it and just
> want to get it merged :)
:)
>
> I think you could expand it a bit, this list would cover the vast bulk
> of branch types for us:
>
>    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 */
>
> cheers

OK, accept! Use 4 bits for above branch types and we can reserve 5 for 
potential future types.

Thanks
Jin Yao