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Message-ID: <ca559765-0f07-b187-bdcd-826dcd99a312@arm.com>
Date: Thu, 13 Jul 2023 13:00:55 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: James Clark <james.clark@....com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Adrian Hunter <adrian.hunter@...el.com>,
Thomas Gleixner <tglx@...utronix.de>,
Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>, Will Deacon <will@...nel.org>,
Kan Liang <kan.liang@...ux.intel.com>,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-perf-users@...r.kernel.org, irogers@...gle.com
Subject: Re: [PATCH 4/4] perf: Remove unused PERF_PMU_CAP_HETEROGENEOUS_CPUS
capability
On 7/11/23 19:45, James Clark wrote:
>
>
> On 11/07/2023 13:10, Anshuman Khandual wrote:
>>
>>
>> On 7/10/23 17:51, James Clark wrote:
>>> Since commit bd2756811766 ("perf: Rewrite core context handling") the
>>> relationship between perf_event_context and PMUs has changed so that
>>> the error scenario that PERF_PMU_CAP_HETEROGENEOUS_CPUS originally
>>> silenced no longer exists.
>>>
>>> Remove the capability to avoid confusion that it actually influences
>>> any perf core behavior. This change should be a no-op.
>>>
>>> Signed-off-by: James Clark <james.clark@....com>
>>> ---
>>> include/linux/perf_event.h | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
>>> index d5628a7b5eaa..3f4d941fd6c5 100644
>>> --- a/include/linux/perf_event.h
>>> +++ b/include/linux/perf_event.h
>>> @@ -288,7 +288,7 @@ struct perf_event_pmu_context;
>>> #define PERF_PMU_CAP_EXTENDED_REGS 0x0008
>>> #define PERF_PMU_CAP_EXCLUSIVE 0x0010
>>> #define PERF_PMU_CAP_ITRACE 0x0020
>>> -#define PERF_PMU_CAP_HETEROGENEOUS_CPUS 0x0040
>>> +/* Unused 0x0040 */
>>
>> Small nit, "Unused" marking might not be required here.
>>
>
> But then it would be very easy to miss that there is a free bit if I
> don't leave the comment. Is it really better without it?
>
> I could shift all the following ones down by one bit, but it would be a
Sounds as a better option IMHO.
> lot of work to make sure that nobody has hard coded some check for one
> of the bits instead of using the define somewhere.
These are not user visible ABI and hence defined in include/linux/perf_event.h
to be used by drivers registering a PMU for capability enumeration. I am just
wondering why they might have been hard coded any where ?
>
>>> #define PERF_PMU_CAP_NO_EXCLUDE 0x0080
>>> #define PERF_PMU_CAP_AUX_OUTPUT 0x0100
>>> #define PERF_PMU_CAP_EXTENDED_HW_TYPE 0x0200
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