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

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Message-ID: <20090507205357.1be739e1@lxorguk.ukuu.org.uk>
Date:	Thu, 7 May 2009 20:53:57 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Christoph Lameter <cl@...ux.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	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>
Subject: Re: [PATCH] x86: Reduce the default HZ value

On Thu, 7 May 2009 14:12:15 -0400 (EDT)
Christoph Lameter <cl@...ux.com> wrote:

> To get back to the main point: I agree with Alok that the default HZ needs
> to be as low as possible. The remaining justification is the load
> balancing and possible context switching between multiple tasks contenting
> for a processor.
> 
> Is it enough if this occurs 100 times per second?

I would like to see evidence that it is, and by evidence I don't mean
"our virtual machine manager runs better" but good evidence that it isn't
affecting performance of any games, applications, video suites etc -
because we know it did in the past.

Even then its pointlessly jumping up and down and changing stuff rather
than fixing the real problem - which is jiffies.

Alan
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