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

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Date:	Wed, 26 Aug 2015 15:12:25 +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:
> @@ -295,6 +317,16 @@ 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));
> +	}
> +

pmu::add should call pmu::start when PERF_EF_START, without that it
should not start the counter, only schedule it.

(although currently all pmu::add() calls will have EF_START set)

>  	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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