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

[Jin, Yao]

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 */

Thanks
Jin Yao