Messages in this thread Patch in this message | | | Date | Fri, 13 Jan 2023 09:45:22 +0530 | Subject | Re: [PATCH V7 3/6] arm64/perf: Add branch stack support in struct arm_pmu | From | Anshuman Khandual <> |
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On 1/12/23 19:24, Mark Rutland wrote: > On Thu, Jan 05, 2023 at 08:40:36AM +0530, Anshuman Khandual wrote: >> This updates 'struct arm_pmu' for branch stack sampling support later. This >> adds a new 'features' element in the structure to track supported features, >> and another 'private' element to encapsulate implementation attributes on a >> given 'struct arm_pmu'. These updates here will help in tracking any branch >> stack sampling support, which is being added later. This also adds a helper >> arm_pmu_branch_stack_supported(). >> >> This also enables perf branch stack sampling event on all 'struct arm pmu', >> supporting the feature but after removing the current gate that blocks such >> events unconditionally in armpmu_event_init(). Instead a quick probe can be >> initiated via arm_pmu_branch_stack_supported() to ascertain the support. >> >> Cc: Catalin Marinas <catalin.marinas@arm.com> >> Cc: Will Deacon <will@kernel.org> >> Cc: Mark Rutland <mark.rutland@arm.com> >> Cc: linux-arm-kernel@lists.infradead.org >> Cc: linux-kernel@vger.kernel.org >> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> >> --- >> drivers/perf/arm_pmu.c | 3 +-- >> include/linux/perf/arm_pmu.h | 9 +++++++++ >> 2 files changed, 10 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c >> index 14a3ed3bdb0b..a85b2d67022e 100644 >> --- a/drivers/perf/arm_pmu.c >> +++ b/drivers/perf/arm_pmu.c >> @@ -510,8 +510,7 @@ static int armpmu_event_init(struct perf_event *event) >> !cpumask_test_cpu(event->cpu, &armpmu->supported_cpus)) >> return -ENOENT; >> >> - /* does not support taken branch sampling */ >> - if (has_branch_stack(event)) >> + if (has_branch_stack(event) && !arm_pmu_branch_stack_supported(armpmu)) >> return -EOPNOTSUPP; >> >> return __hw_perf_event_init(event); >> diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h >> index 2a9d07cee927..64e1b2594025 100644 >> --- a/include/linux/perf/arm_pmu.h >> +++ b/include/linux/perf/arm_pmu.h >> @@ -80,11 +80,14 @@ enum armpmu_attr_groups { >> ARMPMU_NR_ATTR_GROUPS >> }; >> >> +#define ARM_PMU_BRANCH_STACK BIT(0) >> + >> struct arm_pmu { >> struct pmu pmu; >> cpumask_t supported_cpus; >> char *name; >> int pmuver; >> + int features; >> irqreturn_t (*handle_irq)(struct arm_pmu *pmu); >> void (*enable)(struct perf_event *event); >> void (*disable)(struct perf_event *event); > > Hmm, we already have the secure_access field separately. How about we fold that > in and go with: > > unsigned int secure_access : 1, > has_branch_stack : 1;
Something like this would work, but should we use __u32 instead of unsigned int to ensure 32 bit width ?
- bool secure_access; /* 32-bit ARM only */ + unsigned int secure_access : 1, /* 32-bit ARM only */ + has_branch_stack: 1, + reserved : 31;
> > ... that way we have one way to manage flags, we don't need to allocate the > bits, and the bulk of the existing code for secure_access can stay as-is.
Right, the changed code also builds on arm32 without any code change.
> >> @@ -119,8 +122,14 @@ struct arm_pmu { >> >> /* Only to be used by ACPI probing code */ >> unsigned long acpi_cpuid; >> + void *private; > > Does this need to be on the end of struct arm_pmu, or can it be placed earlier?
This additional 'private' attribute structure sticking out from struct arm_pmu should be at the end. But is there any benefit moving this earlier ?
> > The line spacing makes it look like the ACPI comment applies to 'private', > which isn't the case.
Sure, will add the following comment, and a space in between.
diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h index f60f7e01acae..c0a090ff7991 100644 --- a/include/linux/perf/arm_pmu.h +++ b/include/linux/perf/arm_pmu.h @@ -130,6 +130,8 @@ struct arm_pmu { /* Only to be used by ACPI probing code */ unsigned long acpi_cpuid; + + /* Implementation specific attributes */ void *private; };
>> }; >> >> +static inline bool arm_pmu_branch_stack_supported(struct arm_pmu *armpmu) >> +{ >> + return armpmu->features & ARM_PMU_BRANCH_STACK; >> +} > > With the above, this would become: > > static inline bool arm_pmu_branch_stack_supported(struct arm_pmu *armpmu) > { > return armpmu->has_branch_stack; > }
Right, will change this helper as required.
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