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Message-ID: <6143e1cd-4db7-d980-a189-b9b06f99d7c4@arm.com>
Date: Tue, 11 Jul 2023 15:15:55 +0100
From: James Clark <james.clark@....com>
To: Anshuman Khandual <anshuman.khandual@....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 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
lot of work to make sure that nobody has hard coded some check for one
of the bits instead of using the define somewhere.
>> #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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