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Date: Wed, 15 Nov 2023 09:37:36 +0000
From: James Clark <james.clark@....com>
To: Anshuman Khandual <anshuman.khandual@....com>
Cc: Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
Marc Zyngier <maz@...nel.org>,
Suzuki Poulose <suzuki.poulose@....com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
linux-perf-users@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
will@...nel.org, catalin.marinas@....com, mark.rutland@....com
Subject: Re: [V14 3/8] drivers: perf: arm_pmuv3: Enable branch stack sampling
framework
On 15/11/2023 05:44, Anshuman Khandual wrote:
> On 11/14/23 15:28, James Clark wrote:
>>
>>
>> On 14/11/2023 05:13, Anshuman Khandual wrote:
>>> Branch stack sampling support i.e capturing branch records during execution
>>> in core perf, rides along with normal HW events being scheduled on the PMU.
>>> This prepares ARMV8 PMU framework for branch stack support on relevant PMUs
>>> with required HW implementation.
>>>
>>
>> [...]
>>
>>> - All armv8pmu_branch_xxxx() stub definitions have been moved inside
>>> include/linux/perf/arm_pmuv3.h for easy access from both arm32 and
>>> arm64 platforms
>>>
>>
>> This causes lots of W=1 build errors because the prototypes are in
>> arm_pmuv3.h, but arm_brbe.c doesn't include it.
>
> I guess these are the W=1 warnings you mentioned above.
>
> drivers/perf/arm_brbe.c:11:6: warning: no previous prototype for ‘armv8pmu_branch_reset’ [-Wmissing-prototypes]
> 11 | void armv8pmu_branch_reset(void)
> | ^~~~~~~~~~~~~~~~~~~~~
> drivers/perf/arm_brbe.c:190:6: warning: no previous prototype for ‘armv8pmu_branch_save’ [-Wmissing-prototypes]
> 190 | void armv8pmu_branch_save(struct arm_pmu *arm_pmu, void *ctx)
> | ^~~~~~~~~~~~~~~~~~~~
> drivers/perf/arm_brbe.c:236:6: warning: no previous prototype for ‘armv8pmu_branch_attr_valid’ [-Wmissing-prototypes]
> 236 | bool armv8pmu_branch_attr_valid(struct perf_event *event)
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/perf/arm_brbe.c:269:5: warning: no previous prototype for ‘armv8pmu_task_ctx_cache_alloc’ [-Wmissing-prototypes]
> 269 | int armv8pmu_task_ctx_cache_alloc(struct arm_pmu *arm_pmu)
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/perf/arm_brbe.c:279:6: warning: no previous prototype for ‘armv8pmu_task_ctx_cache_free’ [-Wmissing-prototypes]
> 279 | void armv8pmu_task_ctx_cache_free(struct arm_pmu *arm_pmu)
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/perf/arm_brbe.c:303:6: warning: no previous prototype for ‘armv8pmu_branch_probe’ [-Wmissing-prototypes]
> 303 | void armv8pmu_branch_probe(struct arm_pmu *armpmu)
> | ^~~~~~~~~~~~~~~~~~~~~
> drivers/perf/arm_brbe.c:449:6: warning: no previous prototype for ‘armv8pmu_branch_enable’ [-Wmissing-prototypes]
> 449 | void armv8pmu_branch_enable(struct arm_pmu *arm_pmu)
> | ^~~~~~~~~~~~~~~~~~~~~~
> drivers/perf/arm_brbe.c:474:6: warning: no previous prototype for ‘armv8pmu_branch_disable’ [-Wmissing-prototypes]
> 474 | void armv8pmu_branch_disable(void)
> | ^~~~~~~~~~~~~~~~~~~~~~~
> drivers/perf/arm_brbe.c:717:6: warning: no previous prototype for ‘armv8pmu_branch_read’ [-Wmissing-prototypes]
> 717 | void armv8pmu_branch_read(struct pmu_hw_events *cpuc, struct perf_event *event)
>
> Branch helpers are used in ARM PMU V3 driver i.e drivers/perf/arm_pmuv3.c.
> Whether the actual BRBE helper definitions, or their fallback stubs (when
> CONFIG_ARM64_BRBE is not enabled), need to be accessible from arm_pmuv3.c
> driver not from brbe.c implementations itself.
>
>>
>> It seems like the main reason you can't include arm_brbe.h in arm32 code
>> is because there are a load of inline functions and references to
>> registers in there. But these are only used in arm_brbe.c, so they don't
>
> Right, arm32 should not be exposed to BRBE internals via arm_brbe.h header.
>
>> need to be in the header anyway.
>
> Right, these are only used in arm_brbe.c
>
>>
>> If you removed the code from the header and moved it to the source file
>> you could move the brbe prototypes to the brbe header and it would be a
>> bit cleaner and more idiomatic.
>
> Alight, how about the following changes - build tested on arm32 and arm64.
>
> - Move BRBE helpers from arm_brbe.h into arm_brbe.c
> - Move armv8_pmu_xxx() declaration inside arm_brbe.h for arm64 (CONFIG_ARM64_BRBE)
> - Move armv8_pmu_xxx() stub definitions inside arm_pmuv3.c for arm32 (!CONFIG_ARM64_BRBE)
> - Include arm_brbe.h header both in arm_pmuv3.c and arm_brbe.c
Agree to them all except:
- Move armv8_pmu_xxx() stub definitions inside arm_pmuv3.c for arm32
(!CONFIG_ARM64_BRBE)
Normally you put the stubs right next to the prototypes with #else, so
in this case both would be in arm_brbe.h. Not sure what the reason for
splitting them here is? You already said "include arm_brbe.h in
arm_pmuv3.c", so that covers arm32 too.
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