linux-kernel - Re: [PATCH v3 3/6] ARCv2: perf: Support sampling events using overflow interrupts

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Date:	Wed, 26 Aug 2015 15:07:52 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexey Brodkin <Alexey.Brodkin@...opsys.com>
Cc:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	Vineet.Gupta1@...opsys.com, arc-linux-dev@...opsys.com,
	arnd@...db.de, Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [PATCH v3 3/6] ARCv2: perf: Support sampling events using
 overflow interrupts

On Mon, Aug 24, 2015 at 05:20:20PM +0300, Alexey Brodkin wrote:
> @@ -139,9 +141,11 @@ static int arc_pmu_event_init(struct perf_event *event)
>  	struct hw_perf_event *hwc = &event->hw;
>  	int ret;
>  
> -	hwc->sample_period  = arc_pmu->max_period;
> -	hwc->last_period = hwc->sample_period;
> -	local64_set(&hwc->period_left, hwc->sample_period);
> +	if (!is_sampling_event(event)) {
> +		hwc->sample_period  = arc_pmu->max_period;
> +		hwc->last_period = hwc->sample_period;
> +		local64_set(&hwc->period_left, hwc->sample_period);
> +	}

So here we set a max_period sample period for !sampling events such that
we can properly deal with (short) counter overflow and accumulate into a
64bit value.

>  	switch (event->attr.type) {
>  	case PERF_TYPE_HARDWARE:
> @@ -243,6 +247,11 @@ static void arc_pmu_start(struct perf_event *event, int flags)
>  
>  	arc_pmu_event_set_period(event);
>  
> +	/* Enable interrupt for this counter */
> +	if (is_sampling_event(event))
> +		write_aux_reg(ARC_REG_PCT_INT_CTRL,
> +			      read_aux_reg(ARC_REG_PCT_INT_CTRL) | (1 << idx));
> +

Yet here you fail to actually enable the interrupt for the non sampling
events, which makes the above not work.

>  	/* enable ARC pmu here */
>  	write_aux_reg(ARC_REG_PCT_INDEX, idx);
>  	write_aux_reg(ARC_REG_PCT_CONFIG, hwc->config);
--
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