On 6/24/2011 6:22 PM, Premi, Sanjeev wrote:
-----Original Message-----
From: Shilimkar, Santosh
Sent: Friday, June 24, 2011 6:16 PM
To: Russell King - ARM Linux
Cc: Premi, Sanjeev; linux-omap@xxxxxxxxxxxxxxx;
linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [PATCH 2/2] omap2+: pm: cpufreq: Fix
loops_per_jiffy calculation
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@xxxxxxxxxxxxxxxx]
Sent: Friday, June 24, 2011 4:14 PM
To: Premi, Sanjeev
Cc: linux-omap@xxxxxxxxxxxxxxx;
linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
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.
[sp] I did read the code but took long to understand most of it.
Hence patch 1 of this series.
I already accepted that I didn't notice definition of adjust_jiffies.
...call it perils of leaving job half-done across a good-night-sleep!
As is, the calculations of UP are incorrect... which I was fixing.
Anyway, I have an updated patch - currently testing with CONFIG_SMP
enabled. Will be posting soon.
I can imagine what you are gonna post based on Russell comment, but will
wait for your patch before commenting.
Regards
Santosh
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