Messages in this thread Patch in this message | | | Date | Thu, 8 Jun 2023 11:13:24 +0100 | Subject | Re: [PATCH V11 05/10] arm64/perf: Add branch stack support in ARMV8 PMU | From | Suzuki K Poulose <> |
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On 06/06/2023 11:34, Anshuman Khandual wrote: > > > On 6/5/23 17:35, Mark Rutland wrote: >> On Wed, May 31, 2023 at 09:34:23AM +0530, Anshuman Khandual 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. >> >> This generally looks good, but I have a few comments below. >> >> [...] >> >>> +static inline bool armv8pmu_branch_valid(struct perf_event *event) >>> +{ >>> + WARN_ON_ONCE(!has_branch_stack(event)); >>> + return false; >>> +} >> >> IIUC this is for validating the attr, so could we please name this >> armv8pmu_branch_attr_valid() ? > > Sure, will change the name and updated call sites. > >> >> [...] >> >>> +static int branch_records_alloc(struct arm_pmu *armpmu) >>> +{ >>> + struct pmu_hw_events *events; >>> + int cpu; >>> + >>> + for_each_possible_cpu(cpu) {
Shouldn't this be supported_pmus ? i.e. for_each_cpu(cpu, &armpmu->supported_cpus) {
>>> + events = per_cpu_ptr(armpmu->hw_events, cpu); >>> + events->branches = kzalloc(sizeof(struct branch_records), GFP_KERNEL); >>> + if (!events->branches) >>> + return -ENOMEM;
Do we need to free the allocated branches already ?
>>> + }
May be: int ret = 0;
for_each_cpu(cpu, &armpmu->supported_cpus) { events = per_cpu_ptr(armpmu->hw_events, cpu); events->branches = kzalloc(sizeof(struct branch_records), GFP_KERNEL); if (!events->branches) { ret = -ENOMEM; break; } }
if (!ret) return 0;
for_each_cpu(cpu, &armpmu->supported_cpus) { events = per_cpu_ptr(armpmu->hw_events, cpu); if (!events->branches) break; kfree(events->branches); } return ret; >>> + return 0; >> >> This leaks memory if any allocation fails, and the next patch replaces this >> code entirely. > > Okay. > >> >> Please add this once in a working state. Either use the percpu allocation >> trick in the next patch from the start, or have this kzalloc() with a >> corresponding kfree() in an error path. > > I will change branch_records_alloc() as suggested in the next patch's thread > and fold those changes here in this patch. > >> >>> } >>> >>> 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; >>> + >>> ret = smp_call_function_any(&cpu_pmu->supported_cpus, >>> __armv8pmu_probe_pmu, >>> &probe, 1); >>> if (ret) >>> return ret; >>> >>> + if (arm_pmu_branch_stack_supported(cpu_pmu)) { >>> + ret = branch_records_alloc(cpu_pmu); >>> + if (ret) >>> + return ret; >>> + } else { >>> + armv8pmu_private_free(cpu_pmu); >>> + } >> >> I see from the next patch that "private" is four ints, so please just add that >> to struct arm_pmu under an ifdef CONFIG_ARM64_BRBE. That'll simplify this, and >> if we end up needing more space in future we can consider factoring it out. > > struct arm_pmu { > ........................................ > /* Implementation specific attributes */ > void *private; > } > > private pointer here creates an abstraction for given pmu implementation > to hide attribute details without making it known to core arm pmu layer. > Although adding ifdef CONFIG_ARM64_BRBE solves the problem as mentioned > above, it does break that abstraction. Currently arm_pmu layer is aware > about 'branch records' but not about BRBE in particular which the driver > adds later on. I suggest we should not break that abstraction. > > Instead a global 'static struct brbe_hw_attr' in drivers/perf/arm_brbe.c > can be initialized into arm_pmu->private during armv8pmu_branch_probe(), > which will also solve the allocation-free problem. Also similar helpers > armv8pmu_task_ctx_alloc()/free() could be defined to manage task context > cache i.e arm_pmu->pmu.task_ctx_cache independently. > > But now armv8pmu_task_ctx_alloc() can be called after pmu probe confirms > to have arm_pmu->has_branch_stack. > >> >>> + >>> return probe.present ? 0 : -ENODEV; >>> } >> >> It also seems odd to ceck probe.present *after* checking >> arm_pmu_branch_stack_supported(). > > I will reorganize as suggested below. > >> >> With the allocation removed I think this can be written more clearly as: >> >> | static int armv8pmu_probe_pmu(struct arm_pmu *cpu_pmu) >> | { >> | struct armv8pmu_probe_info probe = { >> | .pmu = cpu_pmu, >> | .present = false, >> | }; >> | int ret; >> | >> | ret = smp_call_function_any(&cpu_pmu->supported_cpus, >> | __armv8pmu_probe_pmu, >> | &probe, 1); >> | if (ret) >> | return ret; > | >> | if (!probe.present) >> | return -ENODEV; >> | >> | if (arm_pmu_branch_stack_supported(cpu_pmu)) >> | ret = branch_records_alloc(cpu_pmu); >> | >> | return ret; >> | }
Could we not simplify this as below and keep the abstraction, since we already have it ?
>> | static int armv8pmu_probe_pmu(struct arm_pmu *cpu_pmu) >> | { >> | struct armv8pmu_probe_info probe = { >> | .pmu = cpu_pmu, >> | .present = false, >> | }; >> | int ret; >> | >> | ret = smp_call_function_any(&cpu_pmu->supported_cpus, >> | __armv8pmu_probe_pmu, >> | &probe, 1); >> | if (ret) >> | return ret; >> | if (!probe.present) >> | return -ENODEV; >> | if (!arm_pmu_branch_stack_supported(cpu_pmu)) >> | return 0; >> | >> | ret = armv8pmu_private_alloc(cpu_pmu); >> | if (ret) >> | return ret; >> | >> | ret = branch_records_alloc(cpu_pmu); >> | if (ret) >> | armv8pmu_private_free(cpu_pmu); >> | >> | return ret; >> | }
Suzuki
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