Re: [PATCH v3 1/7] arm_pmu: Clean up maximum period handling

From: Mark Rutland
Date: Tue Jun 19 2018 - 06:45:13 EST

On Tue, Jun 19, 2018 at 11:15:36AM +0100, Suzuki K Poulose wrote:
> Each PMU defines their max_period of the counter as the maximum
> value that can be counted. Since all the PMU backends support
> 32bit counters by default, let us remove the redundant field.
>
> No functional changes.
>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Reviewed-by: Julien Thierry <julien.thierry@xxxxxxx>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>

Acked-by: Mark Rutland <mark.rutland@xxxxxxx>

Mark.

> ---
> No changes since v2
> ---
> arch/arm/kernel/perf_event_v6.c | 2 --
> arch/arm/kernel/perf_event_v7.c | 1 -
> arch/arm/kernel/perf_event_xscale.c | 2 --
> arch/arm64/kernel/perf_event.c | 1 -
> drivers/perf/arm_pmu.c | 16 ++++++++++++----
> include/linux/perf/arm_pmu.h | 1 -
> 6 files changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/arch/arm/kernel/perf_event_v6.c b/arch/arm/kernel/perf_event_v6.c
> index be42c4f..f64a6bf 100644
> --- a/arch/arm/kernel/perf_event_v6.c
> +++ b/arch/arm/kernel/perf_event_v6.c
> @@ -495,7 +495,6 @@ static void armv6pmu_init(struct arm_pmu *cpu_pmu)
> cpu_pmu->stop = armv6pmu_stop;
> cpu_pmu->map_event = armv6_map_event;
> cpu_pmu->num_events = 3;
> - cpu_pmu->max_period = (1LLU << 32) - 1;
> }
>
> static int armv6_1136_pmu_init(struct arm_pmu *cpu_pmu)
> @@ -546,7 +545,6 @@ static int armv6mpcore_pmu_init(struct arm_pmu *cpu_pmu)
> cpu_pmu->stop = armv6pmu_stop;
> cpu_pmu->map_event = armv6mpcore_map_event;
> cpu_pmu->num_events = 3;
> - cpu_pmu->max_period = (1LLU << 32) - 1;
>
> return 0;
> }
> diff --git a/arch/arm/kernel/perf_event_v7.c b/arch/arm/kernel/perf_event_v7.c
> index 57f01e0..ecca4cd 100644
> --- a/arch/arm/kernel/perf_event_v7.c
> +++ b/arch/arm/kernel/perf_event_v7.c
> @@ -1170,7 +1170,6 @@ static void armv7pmu_init(struct arm_pmu *cpu_pmu)
> cpu_pmu->start = armv7pmu_start;
> cpu_pmu->stop = armv7pmu_stop;
> cpu_pmu->reset = armv7pmu_reset;
> - cpu_pmu->max_period = (1LLU << 32) - 1;
> };
>
> static void armv7_read_num_pmnc_events(void *info)
> diff --git a/arch/arm/kernel/perf_event_xscale.c b/arch/arm/kernel/perf_event_xscale.c
> index 88d1a76..c4f0294 100644
> --- a/arch/arm/kernel/perf_event_xscale.c
> +++ b/arch/arm/kernel/perf_event_xscale.c
> @@ -374,7 +374,6 @@ static int xscale1pmu_init(struct arm_pmu *cpu_pmu)
> cpu_pmu->stop = xscale1pmu_stop;
> cpu_pmu->map_event = xscale_map_event;
> cpu_pmu->num_events = 3;
> - cpu_pmu->max_period = (1LLU << 32) - 1;
>
> return 0;
> }
> @@ -743,7 +742,6 @@ static int xscale2pmu_init(struct arm_pmu *cpu_pmu)
> cpu_pmu->stop = xscale2pmu_stop;
> cpu_pmu->map_event = xscale_map_event;
> cpu_pmu->num_events = 5;
> - cpu_pmu->max_period = (1LLU << 32) - 1;
>
> return 0;
> }
> diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
> index 33147aa..678ecff 100644
> --- a/arch/arm64/kernel/perf_event.c
> +++ b/arch/arm64/kernel/perf_event.c
> @@ -960,7 +960,6 @@ static int armv8_pmu_init(struct arm_pmu *cpu_pmu)
> cpu_pmu->start = armv8pmu_start,
> cpu_pmu->stop = armv8pmu_stop,
> cpu_pmu->reset = armv8pmu_reset,
> - cpu_pmu->max_period = (1LLU << 32) - 1,
> cpu_pmu->set_event_filter = armv8pmu_set_event_filter;
>
> return 0;
> diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
> index a6347d4..6ddc00d 100644
> --- a/drivers/perf/arm_pmu.c
> +++ b/drivers/perf/arm_pmu.c
> @@ -28,6 +28,11 @@
> static DEFINE_PER_CPU(struct arm_pmu *, cpu_armpmu);
> static DEFINE_PER_CPU(int, cpu_irq);
>
> +static inline u64 arm_pmu_max_period(void)
> +{
> + return (1ULL << 32) - 1;
> +}
> +
> static int
> armpmu_map_cache_event(const unsigned (*cache_map)
> [PERF_COUNT_HW_CACHE_MAX]
> @@ -114,8 +119,10 @@ int armpmu_event_set_period(struct perf_event *event)
> struct hw_perf_event *hwc = &event->hw;
> s64 left = local64_read(&hwc->period_left);
> s64 period = hwc->sample_period;
> + u64 max_period;
> int ret = 0;
>
> + max_period = arm_pmu_max_period();
> if (unlikely(left <= -period)) {
> left = period;
> local64_set(&hwc->period_left, left);
> @@ -136,8 +143,8 @@ int armpmu_event_set_period(struct perf_event *event)
> * effect we are reducing max_period to account for
> * interrupt latency (and we are being very conservative).
> */
> - if (left > (armpmu->max_period >> 1))
> - left = armpmu->max_period >> 1;
> + if (left > (max_period >> 1))
> + left = (max_period >> 1);
>
> local64_set(&hwc->prev_count, (u64)-left);
>
> @@ -153,6 +160,7 @@ u64 armpmu_event_update(struct perf_event *event)
> struct arm_pmu *armpmu = to_arm_pmu(event->pmu);
> struct hw_perf_event *hwc = &event->hw;
> u64 delta, prev_raw_count, new_raw_count;
> + u64 max_period = arm_pmu_max_period();
>
> again:
> prev_raw_count = local64_read(&hwc->prev_count);
> @@ -162,7 +170,7 @@ u64 armpmu_event_update(struct perf_event *event)
> new_raw_count) != prev_raw_count)
> goto again;
>
> - delta = (new_raw_count - prev_raw_count) & armpmu->max_period;
> + delta = (new_raw_count - prev_raw_count) & max_period;
>
> local64_add(delta, &event->count);
> local64_sub(delta, &hwc->period_left);
> @@ -402,7 +410,7 @@ __hw_perf_event_init(struct perf_event *event)
> * is far less likely to overtake the previous one unless
> * you have some serious IRQ latency issues.
> */
> - hwc->sample_period = armpmu->max_period >> 1;
> + hwc->sample_period = arm_pmu_max_period() >> 1;
> hwc->last_period = hwc->sample_period;
> local64_set(&hwc->period_left, hwc->sample_period);
> }
> diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h
> index ad54444..12c30a2 100644
> --- a/include/linux/perf/arm_pmu.h
> +++ b/include/linux/perf/arm_pmu.h
> @@ -94,7 +94,6 @@ struct arm_pmu {
> void (*reset)(void *);
> int (*map_event)(struct perf_event *event);
> int num_events;
> - u64 max_period;
> bool secure_access; /* 32-bit ARM only */
> #define ARMV8_PMUV3_MAX_COMMON_EVENTS 0x40
> DECLARE_BITMAP(pmceid_bitmap, ARMV8_PMUV3_MAX_COMMON_EVENTS);
> --
> 2.7.4
>