linux-kernel - Re: [PATCH 12/12] clocksource: Add some debug info about clocksources being registered

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Date:	Wed, 11 Mar 2015 20:16:43 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...emonkey.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Richard Cochran <richardcochran@...il.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 12/12] clocksource: Add some debug info about clocksources
 being registered

On Sat, Mar 7, 2015 at 1:50 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * John Stultz <john.stultz@...aro.org> wrote:
>
>> Print the mask, max_cycles, and max_idle_ns values for clocksources
>> being registered.
>>
>> Cc: Dave Jones <davej@...emonkey.org.uk>
>> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: Richard Cochran <richardcochran@...il.com>
>> Cc: Prarit Bhargava <prarit@...hat.com>
>> Cc: Stephen Boyd <sboyd@...eaurora.org>
>> Cc: Ingo Molnar <mingo@...nel.org>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Signed-off-by: John Stultz <john.stultz@...aro.org>
>> ---
>>  kernel/time/clocksource.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
>> index 3f24bb3..9b75316 100644
>> --- a/kernel/time/clocksource.c
>> +++ b/kernel/time/clocksource.c
>> @@ -697,6 +697,10 @@ void __clocksource_updatefreq_scale(struct clocksource *cs, u32 scale, u32 freq)
>
> So that name should really be something like __clocksource_update_freq_scale(),
> right?

Sure, I can add an extra patch to address that...


>>       cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
>>                                                cs->maxadj, cs->mask,
>>                                                &cs->max_cycles);
>> +
>> +     pr_info("clocksource %s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n",
>> +                     cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns);
>> +
>
> Also, why is this function exported? No in-tree module uses it.

So, its mostly due to the fact that the inline function
__clocksource_updatefreq_hz() in clocksource.h uses it, which may be
used by some clocksources in their enable() hooks. And those
clocksources may be compiled as a module.


> Also, when I read the code, I noticed:
>
> /**
>  * __clocksource_updatefreq_scale - Used update clocksource with new freq
>  * @cs:         clocksource to be registered
>  * @scale:      Scale factor multiplied against freq to get clocksource hz
>  * @freq:       clocksource frequency (cycles per second) divided by scale
>  *
>  * This should only be called from the clocksource->enable() method.
>  *
>  * This *SHOULD NOT* be called directly! Please use the
>  * clocksource_updatefreq_hz() or clocksource_updatefreq_khz helper functions.
>
> One more reason to not export it?
>
> Also, typo in the description.
>
> Plus, one helper function is marked with '()', the other not ...

I'll address that in the new patch as well.

thanks
-john
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