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

[Alexandre Ghiti]

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@xxxxxxxxxxxx>
> > ---
> >   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@xxxxxxxxxxxxxxxx>


Thanks!