linux-kernel - Re: [PATCH] Prevent clockevent event_handler ending up handler

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Message-ID: <alpine.LFD.1.10.0809032058380.3243@apollo.tec.linutronix.de>
Date:	Wed, 3 Sep 2008 21:01:35 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andreas Mohr <andi@...as.de>
cc:	Venki Pallipadi <venkatesh.pallipadi@...el.com>,
	linux-kernel@...r.kernel.org, shaohua.li@...el.com
Subject: Re: [PATCH] Prevent clockevent event_handler ending up
 handler_noop

On Wed, 3 Sep 2008, Andreas Mohr wrote:
> On Wed, Sep 03, 2008 at 07:15:16PM +0200, Thomas Gleixner wrote:
> > On Wed, 3 Sep 2008, Andreas Mohr wrote:
> > > See what such highres-deprived people as myself (PIT, acpi_pm,
> > > _no_ HPET and thus no IRQed highres timer) are doing now,
> > 
> > Err. PIT + acpi_pm works with highres. acpi_pm is a stable clocksource
> > and PIT is not a good, but a usable oneshot timer.
> 
> Hmm. What I'm interested in is longer wakeup timeouts (ACPI C2/C3
> stuff), which would be a problem with PIT (~20 forced wakeups per second)
> but with my new timer that would work.
> Oh, side question: it _is_ easily possible to then disable PIT IRQs
> once my event device is registered, right? Otherwise I could forget
> about power management benefits...

When you register something better than PIT, then the PIT is
disabled completely. No more interrupts from there.

> So as I see it, the most beneficial thing I can do is to provide
> a clock_event_device only.

Right.
 
> Out of interest: how big would you believe the benefit to be?
> (overall system performance gains and ACPI PM benefits)

Hard to tell, your milage can vary.

     tglx

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