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

From: Jin, Yao
Date: Mon Jul 10 2017 - 23:01:11 EST

On 7/11/2017 10:28 AM, Michael Ellerman wrote:
"Jin, Yao" <yao.jin@xxxxxxxxxxxxxxx> 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.

Jin Yao