linux-kernel - Re: [PATCH] x86: Reduce the default HZ value

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Date:	Thu, 07 May 2009 09:37:50 -0700
From:	Alok Kataria <akataria@...are.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Christoph Lameter <cl@...ux.com>, "H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	the arch/x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: Reduce the default HZ value


On Thu, 2009-05-07 at 08:14 -0700, Alan Cox wrote:
> On Thu, 7 May 2009 10:13:52 -0400 (EDT)
> Christoph Lameter <cl@...ux.com> wrote:
> 
> > I think we need to reduce the general tick frequency to be as low as
> > possible. With high resolution timers the tick frequency is just the
> > frequency with which the timer interrupt disturbs a running application.
> > 
> > Are there any benefits remaining from frequent timer interrupts? I would
> > think that 60 HZ would be sufficient.
> 
> 50 works for various european video apps, 60 breaks, 60 works for various
> US video apps, 50 breaks. Now that may have changed with all the select
> stuff being hrtimer based (which I'd missed).

I would have assumed whatever timeout mechanism the video apps use
should have already been converted to hrtimers ? Or are you saying that
they use select stuff which is already hrtimer based and so there
shouldn't be any problem now for video apps ? 

> 
> The tick also still appears to be involved in ntp and in cpu stats where
> a 50Hz tick would mean only 25Hz accuracy on CPU usage etc
> 

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