linux-kernel - Re: [PATCH] sched: generalize CONFIG_IRQ_TIME

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Message-ID: <20120208152457.GN889@n2100.arm.linux.org.uk>
Date:	Wed, 8 Feb 2012 15:24:57 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Dmitry Antipov <dmitry.antipov@...aro.org>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Ingo Molnar <mingo@...hat.com>,
	Venki Pallipadi <venki@...gle.com>,
	linaro-dev@...ts.linaro.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] sched: generalize CONFIG_IRQ_TIME_ACCOUNTING for X86
	and ARM

On Wed, Feb 08, 2012 at 07:15:26AM -0800, Dmitry Antipov wrote:
> On 02/08/2012 05:18 AM, Russell King - ARM Linux wrote:
>> Why are you placing this here?  sched_clock is available from the point
>> that it's registered, which should be before the first sched_clock()
>> call.
>
> This is just because I'm thinking about:
>
> if (read_sched_clock == jiffy_sched_clock_read)
>         setup_sched_clock(jiffy_sched_clock_read, 32, HZ);
> else if (!no_sched_irq_time)
> 	enable_sched_clock_irqtime();
>
> I suppose that "fine granularity task irq time accounting"
> makes no sense if sched_clock() granularity is poor.

Let me put it a different way - is there a reason not to do this in
setup_sched_clock() so that it becomes available as soon as sched_clock()
has been initialized by a platform?
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