linux-kernel - Re: [RFC][PATCH] cpuidle: avoid singing capacitors

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Message-ID: <20080301133127.0a85f319@mjolnir.drzeus.cx>
Date:	Sat, 1 Mar 2008 13:31:27 +0100
From:	Pierre Ossman <drzeus-list@...eus.cx>
To:	lsorense@...lub.uwaterloo.ca (Lennart Sorensen)
Cc:	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Adam Belay <abelay@...ell.com>,
	linux-pm@...ts.linux-foundation.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] cpuidle: avoid singing capacitors

On Fri, 29 Feb 2008 16:44:07 -0500
lsorense@...lub.uwaterloo.ca (Lennart Sorensen) wrote:

> On Fri, Feb 29, 2008 at 07:38:12PM +0100, Pierre Ossman wrote:
> > +/*
> > + * The minimum number of ticks needed to not oscillate faster than
> > + * 500 Hz.
> > + */
> > +#define MIN_DEEP_INTERVAL (HZ / 500)
> 
> What happens here if HZ < 500?  Or does the fact that you have less than
> 500HZ jiffies automatically imply that you can't go to sleep more than
> the jiffy rate times per second?

A low HZ will still go to sleep very often (provided NO_HZ is in effect). But a HZ < 500 makes that number up there turn to zero.  But the check further down makes sure that at least 1 tick passes. So that means it will not enter C3 more often than min(HZ, 500) Hz. Another reason to stop using jiffies.

-- 
     -- Pierre Ossman

  Linux kernel, MMC maintainer        http://www.kernel.org
  PulseAudio, core developer          http://pulseaudio.org
  rdesktop, core developer          http://www.rdesktop.org
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