[PATCHv2] omap2+: pm: cpufreq: Fix loops_per_jiffy calculation

[Premi, Sanjeev]

> -----Original Message-----
> From: Russell King - ARM Linux [mailto:linux at arm.linux.org.uk] 
> Sent: Friday, June 24, 2011 8:42 PM
> To: Premi, Sanjeev
> Cc: linux-omap at vger.kernel.org; linux-arm-kernel at lists.infradead.org
> Subject: Re: [PATCHv2] omap2+: pm: cpufreq: Fix 
> loops_per_jiffy calculation
> 
> Right, thanks for the file.  Here's the patch.
> 
> --- omap2plus-cpufreq.c~	2011-06-24 15:50:32.000000000 +0100
> +++ omap2plus-cpufreq.c	2011-06-24 16:00:08.000000000 +0100
> @@ -44,6 +44,16 @@
>  static char *mpu_clk_name;
>  static struct device *mpu_dev;
>  
> +#ifdef CONFIG_SMP
> +struct lpj_info {
> +	unsigned long	ref;
> +	unsigned int	freq;
> +};
> +
> +static DEFINE_PER_CPU(struct lpj_info, lpj_ref);
> +static struct lpj_info global_lpj_ref;
> +#endif
> +
>  static int omap_verify_speed(struct cpufreq_policy *policy)
>  {
>  	if (!freq_table)
> @@ -109,14 +119,25 @@
>  	freqs.new = omap_getspeed(policy->cpu);
>  
>  #ifdef CONFIG_SMP
> -	/* Adjust jiffies before transition */
> +	/* Adjust per-cpu loops_per_jiffy before transition */
>  	for_each_cpu(i, policy->cpus) {
> -		unsigned long lpj = per_cpu(cpu_data, 
> i).loops_per_jiffy;
> -
> -		per_cpu(cpu_data, i).loops_per_jiffy = 
> cpufreq_scale(lpj,
> -							freqs.old,
> -							freqs.new);
> +		struct lpj_info *lpj = &per_cpu(lpj_ref, i);
> +		if (!lpj->freq) {
> +			lpj->ref = per_cpu(cpu_data, i).loops_per_jiffy;
> +			lpj->freq = freqs.old;
> +		}
> +
> +		per_cpu(cpu_data, i).loops_per_jiffy =
> +			cpufreq_scale(lpj->ref, lpj->freq, freqs.new);
> +	}
> +
> +	/* And don't forget to adjust the global one */
> +	if (!global_lpj_ref.freq) {
> +		global_lpj_ref.ref = loops_per_jiffy;
> +		global_lpj_ref.freq = freqs.old;
>  	}
> +	loops_per_jiffy = cpufreq_scale(global_lpj_ref.ref, 
> global_lpj_ref.freq,
> +					freqs.new);
>  #endif
>  
>  	/* Notify transitions */
> 
> 
> Notice how we adjust _both_ the per-cpu loops_per_jiffy, and that we
> adjust them with reference to the initial values.
> 
> If you adjust lpj with reference to the last, then you _will_ build up
> a progressively bigger and bigger error in the value over time.

Russell,

I definitely didn't see so many things through your comments. But
that may just be reflection of my naivety with SMP!

I am currently testing another patch for beagle - will apply and
test on OMAP3EVM (just to be sure).

Can I include it in my next patch rev?

~sanjeev