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Date: Tue, 21 Nov 2023 14:43:54 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: James Clark <james.clark@....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 11/15/23 15:07, James Clark wrote:
>
>
> 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.
Not any particular strong reason for the split as such, will move these
stubs to the header as well. BRBE header includes <linux/perf/arm_pmu.h>
which causes the following redefinition warning for the pr_fmt().
drivers/perf/arm_brbe.c:11: warning: "pr_fmt" redefined
11 | #define pr_fmt(fmt) "brbe: " fmt
|
In file included from ./include/linux/kernel.h:31,
from ./include/linux/interrupt.h:6,
from ./include/linux/perf/arm_pmu.h:11,
from drivers/perf/arm_brbe.h:10,
from drivers/perf/arm_brbe.c:9:
./include/linux/printk.h:345: note: this is the location of the previous definition
345 | #define pr_fmt(fmt) fmt
Although it should be okay to just drop this custom pr_fmt() from BRBE.
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