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

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Message-ID: <87shi37lmp.fsf@concordia.ellerman.id.au>
Date:   Tue, 11 Jul 2017 12:28:14 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     "Jin\, Yao" <yao.jin@...ux.intel.com>,
        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

"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