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

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Date:	Thu, 7 May 2009 18:09:09 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Christoph Lameter <cl@...ux.com>,
	Alok Kataria <akataria@...are.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, 07 May 2009 12:55:05 -0400
Jeff Garzik <jeff@...zik.org> wrote:

> H. Peter Anvin wrote:
> > Alan Cox wrote:
> >> Hooray - finally someone admits the *real* problem here, and for power
> >> management too. Otherwise known as "referencing jiffies as a variable must
> >> die"
> > 
> > Amen.  Also, "using HZ as a unit of measurement must die, too."
> 
> Love to -- now, what will it be replaced with?
> 
> grep for 'deadline' in drivers/ata/libata* to find an example not so 
> easily converted away from jiffies.

I don't see any.

I do see a complicated interface that appears to actually really want to
implement

		add_timer(&foo->expiry_timer);

and checks against the timer completing. In fact it looks as if all the
stuff in there is really down to

		add a timer
		check if it expired
		check how long until it expires
		delete it

And you might as well measure that in HZ=1000's better known as
"milliseconds"

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