[parisc-linux] Strange delay loop calibration with SMP kernel on UP system
Sat, 12 Apr 2003 18:58:02 +0200
As I was working on 2.5 SMPness on our A500, tausq suggested me to try SMP
kernel on a UP box.
So I deconfigured one CPU on the A500.
The kernel failed miserably, and I rebooted the box with its _original 2.4
SMP kernel_, _without bringing the second CPU back online_.
I repeat: i booted the box with the 2.4 SMP kernel it used to run with 2
CPUs. That's 2.4.20-pa28 fwiw.
What a surprise!
The delay loop calibration gave a completely different value than what I'd
have expected according to previous boots.
A500 configured with 2 CPUs:
Calibrating delay loop... 1097.72 BogoMIPS
A500 configured with 1 CPU:
Calibrating delay loop... 366.18 BogoMIPS
Please mind I'm not talking about "total bogomips".
I'm talking about the calibration that takes place at the very early stage
of the boot process, on 1 CPU (the monarch on SMP systems).
So that has nothing to do with having half bogomips because there's half
That being said, one would have noticed that 1097.72/366.18 ~= 3
Now I wonder, is that normal (I couldn't check on another arch), or is
that some kind of new and unknown bug?
The PA/Linux ESIEE Team