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

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Message-ID: <20170710143737.GC13471@gate.crashing.org>
Date:   Mon, 10 Jul 2017 09:37:42 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Jin, Yao" <yao.jin@...ux.intel.com>,
        Michael Ellerman <mpe@...erman.id.au>, 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

Hi Peter,

On Mon, Jul 10, 2017 at 03:46:58PM +0200, 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.

If we would do that, yes :-)  (We just generate a SIGTRAP instead).

> > 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.

Ah, right, exceptions == interrupts for PowerPC, more terminological
confusion :-)


Segher