linux-kernel - Re: [PATCH v2 4/8] ARCv2: perf: Support sampling events using overflow interrupts

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Message-ID: <20150818221215.GO20948@worktop>
Date:	Wed, 19 Aug 2015 00:12:15 +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 v2 4/8] ARCv2: perf: Support sampling events using
 overflow interrupts

On Wed, Aug 05, 2015 at 06:13:30PM +0300, Alexey Brodkin wrote:
> @@ -319,6 +336,20 @@ static int arc_pmu_add(struct perf_event *event, int flags)
>  	}
>  
>  	write_aux_reg(ARC_REG_PCT_INDEX, idx);
> +
> +	arc_pmu->act_counter[idx] = event;
> +
> +	if (is_sampling_event(event)) {
> +		/* Mimic full counter overflow as other arches do */
> +		write_aux_reg(ARC_REG_PCT_INT_CNTL, (u32)arc_pmu->max_period);
> +		write_aux_reg(ARC_REG_PCT_INT_CNTH,
> +			      (arc_pmu->max_period >> 32));
> +
> +		/* Enable interrupt for this counter */
> +		write_aux_reg(ARC_REG_PCT_INT_CTRL,
> +			      read_aux_reg(ARC_REG_PCT_INT_CTRL) | (1 << idx));
> +	}

*confused* pmu::add should only start on flags & PERF_EF_START, and then
we start with hwc->sample_period, not the max_period.

> +
>  	write_aux_reg(ARC_REG_PCT_CONFIG, 0);
>  	write_aux_reg(ARC_REG_PCT_COUNTL, 0);
>  	write_aux_reg(ARC_REG_PCT_COUNTH, 0);
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