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

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Message-ID: <0d5f93ef-f5c9-5185-c1f6-f176f8f533ea@intel.com>
Date:   Wed, 21 Jun 2017 23:20:03 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
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

On 06/21/2017 08:29 PM, Arnaldo Carvalho de Melo wrote:
> 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?

That seems fine.  Pedantically it should be (INT_MAX + 1U) otherwise it will
be negative on a 32-bit system.

> 
>>> 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
>