[PATCH v6 1/7] perf/core: Define the common branch type classification
yao.jin at linux.intel.com
Tue Jul 11 13:00:55 AEST 2017
On 7/11/2017 10:28 AM, Michael Ellerman wrote:
> "Jin, Yao" <yao.jin at linux.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
>>>> 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
>>>> 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 */
OK, accept! Use 4 bits for above branch types and we can reserve 5 for
potential future types.
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