Re: [PATCH 2/2] omap2+: pm: cpufreq: Fix loops_per_jiffy calculation

[Santosh Shilimkar <santosh.shilimkar@ti.com>]

Sanjeev,

On 6/24/2011 4:21 PM, Russell King - ARM Linux wrote:
> On Fri, Jun 24, 2011 at 04:18:31PM +0530, Premi, Sanjeev wrote:
>>> -----Original Message-----
>>> From: Russell King - ARM Linux [mailto:linux@arm.linux.org.uk]
>>> Sent: Friday, June 24, 2011 4:14 PM
>>> To: Premi, Sanjeev
>>> Cc: linux-omap@vger.kernel.org; linux-arm-kernel@lists.infradead.org
>>> Subject: Re: [PATCH 2/2] omap2+: pm: cpufreq: Fix
>>> loops_per_jiffy calculation
>>>
>>> On Fri, Jun 24, 2011 at 04:05:42PM +0530, Sanjeev Premi wrote:
>>>> Currently, loops_per_jiffy is being calculated before calling
>>>> cpufreq_notify_transition().
>>>>
>>>> However, generic cpufreq driver adjusts the jiffies as well.
>>>> Double adjustment leads to incorrect value being assigned to
>>>> loops_per_jiffy.
>>>
>>> Are you sure the generic cpufreq driver adjusts the per-cpu
>>> loops_per_jiffy
>>> values?  I don't believe it does.
>>
>> Russell,
>>
>> I am quoting the function from drivers/cpufreq/cpufreq.h
>> Follow the arrows:
>
> Let's go to war with quotes then, because clearly you haven't read the code
> properly:
>
> | #ifndef CONFIG_SMP
> ^^^^^^^^^^^^^^^^^^^^^
> | static unsigned long l_p_j_ref;
> | static unsigned int  l_p_j_ref_freq;
> |
> | static void adjust_jiffies(unsigned long val, struct cpufreq_freqs *ci)
> | {
> | 	... code to adjust jiffies ...
> | }
> | #else
> | static inline void adjust_jiffies(unsigned long val, struct cpufreq_freqs *ci)
> | {
> |         return;
> | }
> | #endif
>
> Notice how if CONFIG_SMP is set, adjust_jiffies becomes a no-op.  So if
> CONFIG_SMP=y, loops_per_jiffy will _not_ be scaled by core code.
>
As Russell rightly pointed out, you need to take care of UP/SMP and UP 
OVER SMP.

The generic code updates in only in case of UP build. I thought, the
comment is the code was well explaining that part.

Regards
Santosh