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

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Message-ID: <20170710131049.GA13471@gate.crashing.org>
Date:   Mon, 10 Jul 2017 08:10:50 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     "Jin, Yao" <yao.jin@...ux.intel.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>, acme@...nel.org,
        jolsa@...nel.org, peterz@...radead.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

Hi!

On Mon, Jul 10, 2017 at 07:46:17PM +0800, Jin, Yao wrote:
> 1. We all agree these definitions:
> 
> +	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 */
> +	PERF_BR_SYSCALL		= 7,	/* syscall */
> +	PERF_BR_SYSRET		= 8,	/* syscall return */
> +	PERF_BR_IRET		= 11,	/* return from interrupt */

Do we?  It does not map very well to PowerPC branch types.

> 2. I wish to keep following definitions for x86.
> 
> +	PERF_BR_IRQ		= 9,	/* hw interrupt/trap/fault */
> +	PERF_BR_INT		= 10,	/* sw interrupt */
> 
> 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?  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 also does not follow the lines of "software caused interrupt" vs.
the rest.

> 4. I'd like to add following types for powerpc.
> 
> 	PERF_BR_COND_CALL	/* Conditional call */
> 	PERF_BR_COND_RET	/* Condition return */

Almost all PowerPC branches have a "conditional" version (only "syscall"
and "sysret/iret" do not -- and those last two are the same, just like
PERF_BR_INT seems to be the same as PERF_BR_SYSCALL).

So how should those PERF_BR_* be used?  It cannot be used in an
architecture-neutral interface the way you define it now.

Segher