From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, will@kernel.org,
catalin.marinas@arm.com, Mark Brown <broonie@kernel.org>,
James Clark <james.clark@arm.com>, Rob Herring <robh@kernel.org>,
Marc Zyngier <maz@kernel.org>,
Suzuki Poulose <suzuki.poulose@arm.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
linux-perf-users@vger.kernel.org
Subject: Re: [PATCH V11 05/10] arm64/perf: Add branch stack support in ARMV8 PMU
Date: Tue, 6 Jun 2023 16:04:25 +0530 [thread overview]
Message-ID: <ba396c30-6719-1dfb-77c2-9f7e1715b57c@arm.com> (raw)
In-Reply-To: <ZH3PCqYt/UzoiVx3@FVFF77S0Q05N>
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) {
>> + events = per_cpu_ptr(armpmu->hw_events, cpu);
>> + events->branches = kzalloc(sizeof(struct branch_records), GFP_KERNEL);
>> + if (!events->branches)
>> + return -ENOMEM;
>> + }
>> + 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;
> | }
next prev parent reply other threads:[~2023-06-06 10:35 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-31 4:04 [PATCH V11 00/10] arm64/perf: Enable branch stack sampling Anshuman Khandual
2023-05-31 4:04 ` [PATCH V11 01/10] drivers: perf: arm_pmu: Add new sched_task() callback Anshuman Khandual
2023-06-05 7:26 ` Mark Rutland
2023-05-31 4:04 ` [PATCH V11 02/10] arm64/perf: Add BRBE registers and fields Anshuman Khandual
2023-06-05 7:55 ` Mark Rutland
2023-06-06 4:27 ` Anshuman Khandual
2023-06-13 16:27 ` Mark Rutland
2023-06-14 2:59 ` Anshuman Khandual
2023-05-31 4:04 ` [PATCH V11 03/10] arm64/perf: Add branch stack support in struct arm_pmu Anshuman Khandual
2023-06-05 7:58 ` Mark Rutland
2023-06-06 4:47 ` Anshuman Khandual
2023-05-31 4:04 ` [PATCH V11 04/10] arm64/perf: Add branch stack support in struct pmu_hw_events Anshuman Khandual
2023-06-05 8:00 ` Mark Rutland
2023-05-31 4:04 ` [PATCH V11 05/10] arm64/perf: Add branch stack support in ARMV8 PMU Anshuman Khandual
2023-06-02 2:33 ` Namhyung Kim
2023-06-05 2:43 ` Anshuman Khandual
2023-06-05 12:05 ` Mark Rutland
2023-06-06 10:34 ` Anshuman Khandual [this message]
2023-06-06 10:41 ` Mark Rutland
2023-06-08 10:13 ` Suzuki K Poulose
2023-06-09 4:00 ` Anshuman Khandual
2023-06-09 9:54 ` Suzuki K Poulose
2023-06-09 7:14 ` Anshuman Khandual
2023-05-31 4:04 ` [PATCH V11 06/10] arm64/perf: Enable branch stack events via FEAT_BRBE Anshuman Khandual
2023-06-02 1:45 ` Namhyung Kim
2023-06-05 3:00 ` Anshuman Khandual
2023-06-05 13:43 ` Mark Rutland
2023-06-09 4:30 ` Anshuman Khandual
2023-06-09 12:37 ` Mark Rutland
2023-06-09 4:47 ` Anshuman Khandual
2023-06-09 12:42 ` Mark Rutland
2023-06-09 5:22 ` Anshuman Khandual
2023-06-09 12:47 ` Mark Rutland
2023-06-09 13:15 ` Mark Rutland
2023-06-12 8:35 ` Anshuman Khandual
2023-06-09 13:34 ` James Clark
2023-06-12 10:12 ` Anshuman Khandual
2023-05-31 4:04 ` [PATCH V11 07/10] arm64/perf: Add PERF_ATTACH_TASK_DATA to events with has_branch_stack() Anshuman Khandual
2023-05-31 4:04 ` [PATCH V11 08/10] arm64/perf: Add struct brbe_regset helper functions Anshuman Khandual
2023-06-02 2:40 ` Namhyung Kim
2023-06-05 3:14 ` Anshuman Khandual
2023-06-05 23:49 ` Namhyung Kim
2023-06-13 17:17 ` Mark Rutland
2023-06-14 5:14 ` Anshuman Khandual
2023-06-14 10:59 ` Mark Rutland
2023-05-31 4:04 ` [PATCH V11 09/10] arm64/perf: Implement branch records save on task sched out Anshuman Khandual
2023-05-31 4:04 ` [PATCH V11 10/10] arm64/perf: Implement branch records save on PMU IRQ Anshuman Khandual
2023-06-09 11:13 ` [PATCH V11 00/10] arm64/perf: Enable branch stack sampling Anshuman Khandual
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