linux-kernel - Re: [PATCH v2 3/8] ARCv2: perf: implement "event_set

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Date:	Tue, 18 Aug 2015 19:52:03 +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 3/8] ARCv2: perf: implement "event_set_period" for
 future use with interrupts

On Wed, Aug 05, 2015 at 06:13:29PM +0300, Alexey Brodkin wrote:
> Even though this hardware implementation allows for more flexibility,
> in Linux kernel we decided to mimic behavior of other architectures this
> way:
> 
>  [1] Set limit value as half of counter's max value (to allow counter to
>      run after reaching it limit, see below for more explanation):
>  ---------->8-----------
>  arc_pmu->max_period = (1ULL << counter_size) / 2 - 1ULL;
>  ---------->8-----------

> @@ -317,10 +365,11 @@ static int arc_pmu_device_probe(struct platform_device *pdev)
>  		return -ENOMEM;
>  
>  	arc_pmu->n_counters = pct_bcr.c;
> -	arc_pmu->counter_size = 32 + (pct_bcr.s << 4);
> +	counter_size = 32 + (pct_bcr.s << 4);
> +	arc_pmu->max_period = (1ULL << counter_size) - 1ULL;
>  

I don't see that /2 there..
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