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

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Message-ID: <alpine.DEB.1.10.0905071342250.22107@qirst.com>
Date:	Thu, 7 May 2009 13:50:16 -0400 (EDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Alok Kataria <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>,
	"alan@...rguk.ukuu.org.uk" <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] x86: Reduce the default HZ value

On Thu, 7 May 2009, Peter Zijlstra wrote:

> No it won't, you want fairly decent involuntary preemption rate to keep
> the full service latency at a usable figure.
>
> The problem with scheduling a hrtimer along with tasks is that at high
> context switch rates the timer will never fire but you do pay the
> overhead of programming the hardware each time, something that can be
> about as expensive as the whole context switch itself.

What are high context switch rates? 1000 HZ? Generally it seems that
context switches are bad for cpu caches and thus to be avoided.

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