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

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Date:	Thu, 7 May 2009 10:09:56 -0400 (EDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
cc:	akataria@...are.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 Tue, 5 May 2009, Alan Cox wrote:

> HZ on a tickless system has no meaningful relationship to wakup rates -
> which are what I assume you actually care about.

Linux is not tickless. It only switches off ticks if a processor is idle.

> So do you want to change the precision of poll() and other
> functionality ? or do you want to change the wakeup rates and
> corresponding virtualisation overhead ?

select and poll use timeouts based on high resolution timers.

> What measurements have you done that make you think HZ is relevant in a
> tickless kernel ?

Just reading the code gets you there.


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