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

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Date:	Wed, 2 Oct 2013 13:14:44 -0400
From:	Santosh Shilimkar <santosh.shilimkar@...com>
To:	Will Deacon <will.deacon@....com>
CC:	"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>,
	Stephen Boyd <sboyd@...eaurora.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>
Subject: Re: [PATCH] sched_clock: fix postinit no sched_clock function check

On Wednesday 02 October 2013 01:09 PM, Will Deacon wrote:
> On Wed, Oct 02, 2013 at 05:55:28PM +0100, Santosh Shilimkar wrote:
>> The sched_clock code uses 2 levels of function pointers, sched_clock_func()
>> and read_sched_clock() but the no sched_clock check in postinit() just
>> checks read_sched_clock().
>>
>> This leads to kernel falling back to jiffy based sched clock even in
>> presence of sched_clock_func() which is not desirable.
>>
>> Fix the postinit() check to avoid the issue. Probably the issue is hidden
>> so far on most of the arm SOCs because of already existing sched_clock
>> registrations apart from arch_timer sched_clock. One can reproduce the
>> issue by just have arch_timer as sched_clock
> 
> Isn't this just an issue with the arch timer driver not calling
> setup_sched_clock? Instead, we munge around with sched_clock_func directly,
> which doesn't appear to be the way anybody else deals with this.
> 
I thought about that option as well but was not sure since even in that case
the check is not complete. We just ensure that function is popullated.

> I'm not sure of the history though, so perhaps there's a reason for this...
> 
Am curious as well.

Regards,
Santosh
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