linux-kernel - Re: [PATCH V3 20/37] perf script: Add 'synth' event type for synthesized events

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Date:   Wed, 21 Jun 2017 14:29:11 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Wang Nan <wangnan0@...wei.com>,
        David Ahern <dsahern@...il.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 20/37] perf script: Add 'synth' event type for
 synthesized events

Em Wed, Jun 21, 2017 at 07:41:04PM +0300, Adrian Hunter escreveu:
> On 06/21/2017 04:51 PM, Arnaldo Carvalho de Melo wrote:
> > Em Wed, Jun 21, 2017 at 01:17:19PM +0300, Adrian Hunter escreveu:
> >> +++ b/tools/perf/util/event.h
> >> @@ -252,6 +252,9 @@ enum auxtrace_error_type {
> >>        PERF_AUXTRACE_ERROR_MAX
> >> };
> > 
> >> +/* Attribute type for custom synthesized events */
> >> +#define PERF_TYPE_SYNTH		3000000000
> > 
> > Why don't you make it PERF_TYPE_MAX and bump PERF_TYPE_MAX by one? I.e.
> > this way we have what can be in attr.type in a nice enumeration, can
> > validate it more easily (attr.type < PERF_TYPE_MAX) and will not need to 
> > do those conversions to/from OUTPUT_TYPE_/PERF_TYPE_).
 
> PERF_TYPE_ is dynamically allocated above PERF_TYPE_MAX for PMUs.  Presently
> perf_pmu_register() calls idr_alloc() with end=0 which limits the allocation
> to INT_MAX.

Oh, forgot about that, guess a comment right beside PERF_TYPE_MAX is in
demand :-\

So why not:

/*
 * PERF_TYPE_ is dynamically allocated above PERF_TYPE_MAX for PMUs.  Presently
 * perf_pmu_register() calls idr_alloc() with end=0 which limits the allocation
 * to INT_MAX.
 */
#define PERF_TYPE_SYNTH		(INT_MAX + 1L)

I.e. wouldn't be some arbitrarily huge value, but one right after what
was defined as the area for the dynamicly allocated PERF_TYPE_
"namespace" for PMUs, right?

> > Peter: now its not the PERF_RECORD_ namespace that userspaces want a
> > chunk of, its PERF_TYPE_, which so far has been pretty stable, grabing
> > _one_ for event synthesizing things like Intel PT (and ARM's coresight,
> > I think) directly at include/uapi/linux/perf_event.h's perf_type_id enum
> > looks cleaner, no?

- Arnaldo