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

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Message-ID: <20131002170917.GB30298@mudshark.cambridge.arm.com>
Date:	Wed, 2 Oct 2013 18:09:17 +0100
From:	Will Deacon <will.deacon@....com>
To:	Santosh Shilimkar <santosh.shilimkar@...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 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'm not sure of the history though, so perhaps there's a reason for this...

Will
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