linux-kernel - Re: [PATCH 26/29] x86/perfcounters: introduce max

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Date:	Wed, 29 Apr 2009 13:14:20 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Robert Richter <robert.richter@....com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 26/29] x86/perfcounters: introduce max_period variable


* Robert Richter <robert.richter@....com> wrote:

> In x86 pmus the allowed counter period to programm differs. This
> introduces a max_period value and allows the generic implementation
> for all models to check the max period.
> 
> Signed-off-by: Robert Richter <robert.richter@....com>
> ---
>  arch/x86/kernel/cpu/perf_counter.c |   20 ++++++++++++--------
>  1 files changed, 12 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
> index a8a53ab..4b8715b 100644
> --- a/arch/x86/kernel/cpu/perf_counter.c
> +++ b/arch/x86/kernel/cpu/perf_counter.c
> @@ -54,6 +54,7 @@ struct x86_pmu {
>  	int		num_counters_fixed;
>  	int		counter_bits;
>  	u64		counter_mask;
> +	u64		max_period;
>  };
>  
>  static struct x86_pmu x86_pmu __read_mostly;
> @@ -279,14 +280,8 @@ static int __hw_perf_counter_init(struct perf_counter *counter)
>  		hwc->nmi = 1;
>  
>  	hwc->irq_period		= hw_event->irq_period;
> -	/*
> -	 * Intel PMCs cannot be accessed sanely above 32 bit width,
> -	 * so we install an artificial 1<<31 period regardless of
> -	 * the generic counter period:
> -	 */
> -	if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL)
> -		if ((s64)hwc->irq_period <= 0 || hwc->irq_period > 0x7FFFFFFF)
> -			hwc->irq_period = 0x7FFFFFFF;
> +	if ((s64)hwc->irq_period <= 0 || hwc->irq_period > x86_pmu.max_period)
> +		hwc->irq_period = x86_pmu.max_period;

btw., should hwc->irq_period perhaps have an s64 type?

	Ingo
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