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

Adrian Hunter
2017-06-21T20:26:17Z

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
>