Re: [PATCH v2 06/10] drivers: perf: Implement perf event mmap support in the legacy backend

Alexandre Ghiti
2023-06-15T07:39:10Z

On 31/05/2023 16:27, Andrew Jones wrote:
> On Fri, May 12, 2023 at 10:53:17AM +0200, Alexandre Ghiti wrote:
>> Implement the needed callbacks in the legacy driver so that we can
>> directly access the counters through perf in userspace.
>>
>> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
>> ---
>> drivers/perf/riscv_pmu_legacy.c | 28 ++++++++++++++++++++++++++++
>> 1 file changed, 28 insertions(+)
>>
>> diff --git a/drivers/perf/riscv_pmu_legacy.c b/drivers/perf/riscv_pmu_legacy.c
>> index ffe09d857366..f0f5bd856f66 100644
>> --- a/drivers/perf/riscv_pmu_legacy.c
>> +++ b/drivers/perf/riscv_pmu_legacy.c
>> @@ -74,6 +74,31 @@ static void pmu_legacy_ctr_start(struct perf_event *event, u64 ival)
>> local64_set(&hwc->prev_count, initial_val);
>> }
>>
>> +static uint8_t pmu_legacy_csr_index(struct perf_event *event)
>> +{
>> + return event->hw.idx;
>> +}
>> +
>> +static void pmu_legacy_event_mapped(struct perf_event *event, struct mm_struct *mm)
>> +{
>> + /* In legacy mode, the first 3 CSRs are available. */
> Shouldn't this be
>
> /* In legacy mode, the first and third CSR are available. */
>
> ?

Yes, I guess this comment is not right in this context, so I'll remove
the comment entirely as it does bring much.

>> + if (event->attr.config != PERF_COUNT_HW_CPU_CYCLES &&
>> + event->attr.config != PERF_COUNT_HW_INSTRUCTIONS)
>> + return;
>> +
>> + event->hw.flags |= PERF_EVENT_FLAG_USER_READ_CNT;
>> +}
>> +
>> +static void pmu_legacy_event_unmapped(struct perf_event *event, struct mm_struct *mm)
>> +{
>> + /* In legacy mode, the first 3 CSRs are available. */
> same comment
>
>> + if (event->attr.config != PERF_COUNT_HW_CPU_CYCLES &&
>> + event->attr.config != PERF_COUNT_HW_INSTRUCTIONS)
>> + return;
>> +
>> + event->hw.flags &= ~PERF_EVENT_FLAG_USER_READ_CNT;
>> +}
>> +
>> /*
>> * This is just a simple implementation to allow legacy implementations
>> * compatible with new RISC-V PMU driver framework.
>> @@ -94,6 +119,9 @@ static void pmu_legacy_init(struct riscv_pmu *pmu)
>> pmu->ctr_get_width = NULL;
>> pmu->ctr_clear_idx = NULL;
>> pmu->ctr_read = pmu_legacy_read_ctr;
>> + pmu->event_mapped = pmu_legacy_event_mapped;
>> + pmu->event_unmapped = pmu_legacy_event_unmapped;
>> + pmu->csr_index = pmu_legacy_csr_index;
>>
>> perf_pmu_register(&pmu->pmu, RISCV_PMU_LEGACY_PDEV_NAME, PERF_TYPE_RAW);
>> }
>> --
>> 2.37.2
>>
> Otherwise,
>
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

Thanks!