linux-kernel - Re: [patch] make pit clocksource continuous

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Date:	Sun, 13 May 2007 19:36:12 +0200
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Stas Sergeev <stsp@...et.ru>
Cc:	Linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: [patch] make pit clocksource continuous

On Sun, 2007-05-13 at 21:23 +0400, Stas Sergeev wrote:
> Hello.
> 
> Thomas Gleixner wrote:
> >> Does this mean that on even an older
> >> boards (without acpi at all) the hrtimers
> >> won't work?
> > Not if PIT is the only clocksource available.
> So you mean it can work without both the
> pm_timer and hpet? Sorry for bothering you
> too much, but I am trying to use the hrtimers
> in my driver module, so I'd like to know all
> the corner-cases.

It does _NOT_ work without pm_timer or hpet for the reasons explained
before. 

When PIT is the only clocksource in the system, i.e. no HPET and no
PM_TIMER is available, then highres and dynticks are disabled.

> How can I test that situation when the hrtimers
> work only with PIT? Apparently disabling the
> pm_timer and hpet in config doesn't help testing
> it at all, since it simply refuses to work then.

It is supposed to refuse to switch to highres / dyntick when you
disabled pm_timer and hpet.

> Should I use hrtimer_get_res() to see if the
> hrtimers are available, or is there any better way?

hrtimer_get_res() works, but I have no idea why you need hrtimers in
your driver at all.

	tglx


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