Re: Kernel reports 4 CPUS instead of 2...

From: Mark Cuss (
Date: Wed Oct 16 2002 - 14:44:47 EST

Speaking of performance.... :)

Has anyone done any testing on a dual CPU configuration like this? I've
been testing this box with both the RedHat 8 Stock Kernel (2.4.18.something)
and 2.4.19 from Currently, I can't make the thing perform
anywhere near as fast as my Dual PIII 1 Ghz box (running 2.4.7 for the last
325 days...) . I've been compiling the same block of code on both the
machines and comparing the times. The PIII box is around 7 s, while the new
Xeon Box is 13 or 14s...

My thinking was that since the CPUs are much faster, and the FSB is faster,
and the disk controller is faster, that the computer would be faster.

The hardware is obviously faster, I'm sure its just something I've done
wrong in the kernel configuration... If anyone has any advice or words of
wisdom, I'd really appreciate them...

Thanks in advance,


----- Original Message -----
From: "James Cleverdon" <>
To: <>; "Samuel Flory" <>
Cc: "Mark Cuss" <>; <>
Sent: Wednesday, October 16, 2002 1:28 PM
Subject: Re: Kernel reports 4 CPUS instead of 2...

> On Wednesday 16 October 2002 10:54 am, Richard B. Johnson wrote:
> > On Wed, 16 Oct 2002, Samuel Flory wrote:
> > > >On Wed, 16 Oct 2002, Mark Cuss wrote:
> > > >
> > > >This is the correct behavior. If you don't like this, you can
> > > >swap motherboards with me ;) Otherwise, grin and bear it!
> > >
> > > Wouldn't it be easier just to turn off the hypertreading or jackson
> > > tech option in the bios ;-)
> >
> > Why would you ever want to turn it off? You paid for a CPU with
> > two execution units and you want to disable one? This makes
> > no sense unless you are using Windows/2000/Professional, which
> > will trash your disks and all their files if you have two
> > or more CPUs (true).
> No, you're thinking of IBM's Power4 chip, which really does have two CPU
> on one chip, sharing only the L2 cache.
> The P4 hyperthreading shares just about all CPU resources between the two
> threads of execution. There are only separate registers, local APIC, and
> some other minor logic for each "CPU" to call its own. All execution
> are demand shared between them. (The new "pause" opcode, rep nop, allows
> half to yield resources to the other half.)
> That's why typical job mixes only get around 20% improvement. Even
> benchmarks, which run only integer code on one side and floating point on
> other only get around a 40% boost. The P4 just doesn't have all that many
> execution units to go around. Future chips will probably do better.
> > 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.
> --
> James Cleverdon
> IBM xSeries Linux Solutions
> {jamesclv(Unix, preferred), cleverdj(Notes)} at us dot ibm dot com
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