linux-kernel - Re: [PATCH] sched_clock: fix postinit no sched

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Date:	Wed, 9 Oct 2013 20:15:29 -0400
From:	Santosh Shilimkar <santosh.shilimkar@...com>
To:	John Stultz <john.stultz@...aro.org>
CC:	Will Deacon <will.deacon@....com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"arm@...nel.org" <arm@...nel.org>,
	Russell King <linux@....linux.org.uk>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH] sched_clock: fix postinit no sched_clock function check

On Wednesday 09 October 2013 07:59 PM, John Stultz wrote:
> On 10/02/2013 11:07 AM, Santosh Shilimkar wrote:
>> On Wednesday 02 October 2013 01:48 PM, Will Deacon wrote:
>>> On Wed, Oct 02, 2013 at 06:42:40PM +0100, Stephen Boyd wrote:
>>>> On 10/02/13 10:27, Santosh Shilimkar wrote:
>>>>> Really... I have not created patch out of fun.
>>>>> Its broken on my keystone machine at least where the sched_clock is
>>>>> falling back on jiffy based sched_clock even in presence of arch_timer
>>>>> sched_clock.
>>>> How is that possible? sched_clock_func is only assigned by
>>>> arch/arm/kernel/arch_timer.c when the architected timer is detected and
>>>> sched_clock() in kernel/time/sched_clock.c calls that function pointer
>>>> unconditionally. The only way I see this happening is if the architected
>>>> timer rate is zero.
>>>   ^^^^^^^^^^^^^^^^^^
>>>
>>> *cough* CNTFRQ *cough*
>>>
>> :) CNTFRQ as such is fine. I think the below print mis-lead me mostly. 
>>
>> sched_clock: ARM arch timer >56 bits at 6144kHz, resolution 162ns
>> sched_clock: 32 bits at 100 Hz, resolution 10000000ns, wraps every 4294967286ms
>>
>> So yes, now the subject patch actually just avoids the jiffy sched_clock()
>> registration and nothing else. Even without the patch arch_timer sched_clock
>> will be in use.
> 
> Just wanted to follow up here, as I've not been paying close attention.
> Is this issue then resolved, or is something still needed to be queued
> for 3.12/3.13?
> 
There is no regression as I initially thought. Patch fixes the
miss-leading sched_clock print and also prevents timer to handle 
wrapping which is not needed.

So no big deal and I don't mind if we don't apply it.

Regards,
Santosh

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