Re: [PATCH V11 05/10] arm64/perf: Add branch stack support in ARMV8 PMU
From: Anshuman Khandual
Date: Sun Jun 04 2023 - 22:43:23 EST
Hello Namhyung,
On 6/2/23 08:03, Namhyung Kim wrote:
> On Tue, May 30, 2023 at 9:27 PM Anshuman Khandual
> <anshuman.khandual@xxxxxxx> wrote:
>> This enables support for branch stack sampling event in ARMV8 PMU, checking
>> has_branch_stack() on the event inside 'struct arm_pmu' callbacks. Although
>> these branch stack helpers armv8pmu_branch_XXXXX() are just dummy functions
>> for now. While here, this also defines arm_pmu's sched_task() callback with
>> armv8pmu_sched_task(), which resets the branch record buffer on a sched_in.
>>
>> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
>> Cc: Will Deacon <will@xxxxxxxxxx>
>> Cc: Mark Rutland <mark.rutland@xxxxxxx>
>> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
>> Cc: linux-kernel@xxxxxxxxxxxxxxx
>> Tested-by: James Clark <james.clark@xxxxxxx>
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
>> ---
>> arch/arm64/include/asm/perf_event.h | 33 +++++++++++++
>> drivers/perf/arm_pmuv3.c | 76 ++++++++++++++++++++---------
>> 2 files changed, 86 insertions(+), 23 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/perf_event.h b/arch/arm64/include/asm/perf_event.h
>> index eb7071c9eb34..7548813783ba 100644
>> --- a/arch/arm64/include/asm/perf_event.h
>> +++ b/arch/arm64/include/asm/perf_event.h
>> @@ -24,4 +24,37 @@ extern unsigned long perf_misc_flags(struct pt_regs *regs);
>> (regs)->pstate = PSR_MODE_EL1h; \
>> }
>>
>> +struct pmu_hw_events;
>> +struct arm_pmu;
>> +struct perf_event;
>> +
>> +#ifdef CONFIG_PERF_EVENTS
>> +static inline bool has_branch_stack(struct perf_event *event);
>> +
>> +static inline void armv8pmu_branch_read(struct pmu_hw_events *cpuc, struct perf_event *event)
>> +{
>> + WARN_ON_ONCE(!has_branch_stack(event));
>> +}
>> +
>> +static inline bool armv8pmu_branch_valid(struct perf_event *event)
>> +{
>> + WARN_ON_ONCE(!has_branch_stack(event));
>> + return false;
>> +}
>> +
>> +static inline void armv8pmu_branch_enable(struct perf_event *event)
>> +{
>> + WARN_ON_ONCE(!has_branch_stack(event));
>> +}
>> +
>> +static inline void armv8pmu_branch_disable(struct perf_event *event)
>> +{
>> + WARN_ON_ONCE(!has_branch_stack(event));
>> +}
>> +
>> +static inline void armv8pmu_branch_probe(struct arm_pmu *arm_pmu) { }
>> +static inline void armv8pmu_branch_reset(void) { }
>> +static inline int armv8pmu_private_alloc(struct arm_pmu *arm_pmu) { return 0; }
>> +static inline void armv8pmu_private_free(struct arm_pmu *arm_pmu) { }
>> +#endif
>> #endif
>> diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c
>> index c98e4039386d..86d803ff1ae3 100644
>> --- a/drivers/perf/arm_pmuv3.c
>> +++ b/drivers/perf/arm_pmuv3.c
>> @@ -705,38 +705,21 @@ static void armv8pmu_enable_event(struct perf_event *event)
>> * Enable counter and interrupt, and set the counter to count
>> * the event that we're interested in.
>> */
>> -
>> - /*
>> - * Disable counter
>> - */
>> armv8pmu_disable_event_counter(event);
>> -
>> - /*
>> - * Set event.
>> - */
>> armv8pmu_write_event_type(event);
>> -
>> - /*
>> - * Enable interrupt for this counter
>> - */
>> armv8pmu_enable_event_irq(event);
>> -
>> - /*
>> - * Enable counter
>> - */
>> armv8pmu_enable_event_counter(event);
>> +
>> + if (has_branch_stack(event))
>> + armv8pmu_branch_enable(event);
>> }
>>
>> static void armv8pmu_disable_event(struct perf_event *event)
>> {
>> - /*
>> - * Disable counter
>> - */
>> - armv8pmu_disable_event_counter(event);
>> + if (has_branch_stack(event))
>> + armv8pmu_branch_disable(event);
>>
>> - /*
>> - * Disable interrupt for this counter
>> - */
>> + armv8pmu_disable_event_counter(event);
>> armv8pmu_disable_event_irq(event);
>> }
>>
>> @@ -814,6 +797,11 @@ static irqreturn_t armv8pmu_handle_irq(struct arm_pmu *cpu_pmu)
>> if (!armpmu_event_set_period(event))
>> continue;
>>
>> + if (has_branch_stack(event) && !WARN_ON(!cpuc->branches)) {
>> + armv8pmu_branch_read(cpuc, event);
>> + perf_sample_save_brstack(&data, event, &cpuc->branches->branch_stack);
>> + }
>> +
>> /*
>> * Perf event overflow will queue the processing of the event as
>> * an irq_work which will be taken care of in the handling of
>> @@ -912,6 +900,14 @@ static int armv8pmu_user_event_idx(struct perf_event *event)
>> return event->hw.idx;
>> }
>>
>> +static void armv8pmu_sched_task(struct perf_event_pmu_context *pmu_ctx, bool sched_in)
>> +{
>> + struct arm_pmu *armpmu = to_arm_pmu(pmu_ctx->pmu);
>> +
>> + if (sched_in && arm_pmu_branch_stack_supported(armpmu))
>> + armv8pmu_branch_reset();
>> +}
>> +
>> /*
>> * Add an event filter to a given event.
>> */
>> @@ -982,6 +978,9 @@ static void armv8pmu_reset(void *info)
>> pmcr |= ARMV8_PMU_PMCR_LP;
>>
>> armv8pmu_pmcr_write(pmcr);
>> +
>> + if (arm_pmu_branch_stack_supported(cpu_pmu))
>> + armv8pmu_branch_reset();
>> }
>>
>> static int __armv8_pmuv3_map_event_id(struct arm_pmu *armpmu,
>> @@ -1019,6 +1018,9 @@ static int __armv8_pmuv3_map_event(struct perf_event *event,
>>
>> hw_event_id = __armv8_pmuv3_map_event_id(armpmu, event);
>>
>> + if (has_branch_stack(event) && !armv8pmu_branch_valid(event))
>> + return -EOPNOTSUPP;
>> +
>> /*
>> * CHAIN events only work when paired with an adjacent counter, and it
>> * never makes sense for a user to open one in isolation, as they'll be
>> @@ -1135,6 +1137,21 @@ static void __armv8pmu_probe_pmu(void *info)
>> cpu_pmu->reg_pmmir = read_pmmir();
>> else
>> cpu_pmu->reg_pmmir = 0;
>> + armv8pmu_branch_probe(cpu_pmu);
>> +}
>> +
>> +static int branch_records_alloc(struct arm_pmu *armpmu)
>> +{
>> + struct pmu_hw_events *events;
>> + int cpu;
>> +
>> + for_each_possible_cpu(cpu) {
>> + events = per_cpu_ptr(armpmu->hw_events, cpu);
>> + events->branches = kzalloc(sizeof(struct branch_records), GFP_KERNEL);
>> + if (!events->branches)
>> + return -ENOMEM;
>> + }
>> + return 0;
>> }
>>
>> static int armv8pmu_probe_pmu(struct arm_pmu *cpu_pmu)
>> @@ -1145,12 +1162,24 @@ static int armv8pmu_probe_pmu(struct arm_pmu *cpu_pmu)
>> };
>> int ret;
>>
>> + ret = armv8pmu_private_alloc(cpu_pmu);
>> + if (ret)
>> + return ret;
> Wouldn't it be better to move it under the if statement below
> if it's only needed for branch stack?
armv8pmu_private_alloc() allocates arm_pmu's private structure which stores
the BRBE HW attributes during armv8pmu_branch_probe(), called from this SMP
callback __armv8pmu_probe_pmu(). Hence without the structure being allocated
and assigned, following smp_call_function_any() cannot execute successfully.
armv8pmu_private_alloc()
{
......
Allocates arm_pmu->private as single 'struct brbe_hw_attr'
Allocates arm_pmu->pmu.task_ctx_cache
......
}
__armv8pmu_probe_pmu()
armv8pmu_branch_probe()
brbe_attributes_probe()
{
......
brbe_attr->brbe_version = brbe;
brbe_attr->brbe_format = brbe_get_format(brbidr);
brbe_attr->brbe_cc = brbe_get_cc_bits(brbidr);
brbe_attr->brbe_nr = brbe_get_numrec(brbidr);
......
}
armv8pmu_private_alloc() cannot be moved inside armv8pmu_branch_probe(),
because there cannot be any allocation while being in a SMP call context.
>
>> +
>> ret = smp_call_function_any(&cpu_pmu->supported_cpus,
>> __armv8pmu_probe_pmu,
>> &probe, 1);
>> if (ret)
>> return ret;
> Otherwise you might need to free it here.
>
>> + if (arm_pmu_branch_stack_supported(cpu_pmu)) {
>> + ret = branch_records_alloc(cpu_pmu);
>> + if (ret)
>> + return ret;
> And here too.
Not freeing the arm_pmu's private data, might not be a problem in cases
where either pmu does not support BRBE or pmu probe itself fails. But for
completeness, will change as following.
diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c
index 9725a53d6799..fdbe52913cc7 100644
--- a/drivers/perf/arm_pmuv3.c
+++ b/drivers/perf/arm_pmuv3.c
@@ -1198,13 +1198,17 @@ static int armv8pmu_probe_pmu(struct arm_pmu *cpu_pmu)
ret = smp_call_function_any(&cpu_pmu->supported_cpus,
__armv8pmu_probe_pmu,
&probe, 1);
- if (ret)
+ if (ret) {
+ armv8pmu_private_free(cpu_pmu);
return ret;
+ }
if (arm_pmu_branch_stack_supported(cpu_pmu)) {
ret = branch_records_alloc(cpu_pmu);
- if (ret)
+ if (ret) {
+ armv8pmu_private_free(cpu_pmu);
return ret;
+ }
} else {
armv8pmu_private_free(cpu_pmu);
}