linux-kernel - Re: [PATCH v5 08/11] arm-cci: Provide hook for writing to PMU counters

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Date:	Mon, 11 Jan 2016 10:54:54 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	"Suzuki K. Poulose" <suzuki.poulose@....com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	arm@...nel.org, punit.agrawal@....com, peterz@...radead.org
Subject: Re: [PATCH v5 08/11] arm-cci: Provide hook for writing to PMU
 counters

On Mon, Jan 04, 2016 at 11:54:47AM +0000, Suzuki K. Poulose wrote:
> Add a hook for writing to CCI PMU counters. This callback
> can be used for CCI models which requires some extra work
> to program the PMU counter values. To accommodate group writes
> and single counter writes, the call back accepts a bitmask
> of the counter indices which need to be programmed with the
> given value.
> 
> Cc: Punit Agrawal <punit.agrawal@....com>
> Cc: Mark Rutland <mark.rutland@....com>
> Signed-off-by: Suzuki K. Poulose <suzuki.poulose@....com>
> ---
>  drivers/bus/arm-cci.c |   16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/bus/arm-cci.c b/drivers/bus/arm-cci.c
> index 2f1fcf0..47c9581 100644
> --- a/drivers/bus/arm-cci.c
> +++ b/drivers/bus/arm-cci.c
> @@ -134,6 +134,7 @@ struct cci_pmu_model {
>  	struct event_range event_ranges[CCI_IF_MAX];
>  	int (*validate_hw_event)(struct cci_pmu *, unsigned long);
>  	int (*get_event_idx)(struct cci_pmu *, struct cci_pmu_hw_events *, unsigned long);
> +	void (*write_counters)(struct cci_pmu *, unsigned long *, u32 val);
>  };
>  
>  static struct cci_pmu_model cci_pmu_models[];
> @@ -846,7 +847,15 @@ static void pmu_write_counter(struct perf_event *event, u32 value)
>  		dev_err(&cci_pmu->plat_device->dev, "Invalid CCI PMU counter %d\n", idx);
>  		return;
>  	}
> -	__pmu_write_counter(cci_pmu, value, idx);
> +
> +	if (cci_pmu->model->write_counters) {
> +		unsigned long mask[BITS_TO_LONGS(cci_pmu->num_cntrs)];
> +
> +		memset(mask, 0, BITS_TO_LONGS(cci_pmu->num_cntrs) * sizeof(unsigned long));
> +		set_bit(idx, mask);
> +		cci_pmu->model->write_counters(cci_pmu, mask, value);
> +	} else
> +		__pmu_write_counter(cci_pmu, value, idx);
>  }

It would be much simpler to always log writes here, and only do the real
wirtes in batches when we re-enable the PMU (with appropriate
disable/enable calls in the IRQ handler).

We'd still need special hooks for CCIs which require a special dance to
program them, but all the logic to handle the writes would be in one
place.

This should work, regardless.

Thanks,
Mark.

>  
>  /* Write a value to a given set of counters */
> @@ -861,7 +870,10 @@ static void __pmu_write_counters(struct cci_pmu *cci_pmu, unsigned long *mask, u
>  static void __maybe_unused
>  pmu_write_counters(struct cci_pmu *cci_pmu, unsigned long *mask, u32 value)
>  {
> -	__pmu_write_counters(cci_pmu, mask, value);
> +	if (cci_pmu->model->write_counters)
> +		cci_pmu->model->write_counters(cci_pmu, mask, value);
> +	else
> +		__pmu_write_counters(cci_pmu, mask, value);
>  }
>  
>  static u64 pmu_event_update(struct perf_event *event)
> -- 
> 1.7.9.5
>