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

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Message-ID: <524C60F4.7000802@ti.com>
Date:	Wed, 2 Oct 2013 14:07:48 -0400
From:	Santosh Shilimkar <santosh.shilimkar@...com>
To:	Will Deacon <will.deacon@....com>
CC:	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>,
	John Stultz <john.stultz@...aro.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 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.

Regards,
Santosh
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