(You'd better. I designed the beastie involved.)
{^_-} Joanne, jdow@earthlink.net
----- Original Message -----
From: "Richard B. Johnson" <root@chaos.analogic.com>
To: "Robert Love" <rml@tech9.net>
Cc: "Neil Conway" <nconway.list@ukaea.org.uk>; <linux-kernel@vger.kernel.org>
Sent: Friday, October 18, 2002 12:38
Subject: Re: [PATCH] 2.4: variable HZ
> On 18 Oct 2002, Robert Love wrote:
>
> > On Fri, 2002-10-18 at 07:51, Neil Conway wrote:
> >
> > > I was looking at your jiffies_to_clock_t() macro, and I notice that it
> > > will screw up badly if the user chooses a HZ value that isn't a multiple
> > > of the normal value (e.g. 1000 is OK, 512 isn't).
> >
> > OK, sure, but why specify a power-of-two HZ? There is absolutely no
> > reason to, at least on x86.
> >
> > Want 512? 500 will do just as well and has the benefit of (a) being a
> > multiple of the previous HZ and (b) evenly dividing into our concept of
> > time.
> >
> > Robert Love
> >
>
> At least on ix86, HZ needs to be something that CLOCK_TICK_RATE/LATCH
> comes out fairly close. Remember, LATCH is the divisor for the PIT
> and that PIT gets CLOCK_TICK_RATE for its input. If this number isn't
> fairly 'exact' there will be much jumping of time in the sawtooth
> corrector.
>
> If you are not using ELAN, CLOCK_TICK_RATE is 1193180. If your HZ is
> 100, you have 1193180/100 = 1193.18, not too exact. if you use
> 500, you get 1193180/500 = 2386.36 which has twice as much round-off.
> If you use 1193180/512 = 2330.43, even a higher fractional part.
>
> Cheers,
> Dick Johnson
> Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).
> The US military has given us many words, FUBAR, SNAFU, now ENRON.
> Yes, top management were graduates of West Point and Annapolis.
>
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