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Re: off topic, intel processors





Today, Ariel Biener blurbed:

> I would assume that the calibration loop wasn't properly adjusted for pII.
> If anyone can recall, 486DX4-100 gave better performance that some Pentium
> chips, because of the same thing. Browsing back through the Linux archives
> of that time will reveal an explanation by Linus on this subject.
> 
> Of course, I might also be mistaken. 

and PLP added:

> K6/233, plain default setup, /var/log/syslog:
> Feb  2 21:58:10 plp kernel: Calibrating delay loop.. ok - 466.94
> BogoMIPS


hasn't anyone here read the Bogomips mini-howto? BogoMIPS = Bogus MIPS,
it's not the processor speed, it's a bunch of benchmarks for timing,
that DOES indeed take the architecture as a parameter. every newer CPU
usually gets a lower factor, hence a Pmmx can get a higher rating than a
PII. K6 is still identified as a 486 in many cases AFAIR, therefore the
monstrous rating.

actually, I looked at the howto and it says the opposite of what I
remember, that higher platforms recieve a higher factor... now I'm
confused..

from the howto: 

BogoMips are Linus's invention. The kernel (or was it a device driver?)
needs a timing loop (the time is too short and/or needs to be too exact
for a non-busy-loop method of waiting), which must be calibrated to the
processor speed of the machine. Hence, the kernel measures at boot time
how fast a certain kind of busy loop runs on a computer. "Bogo" comes
from "bogus", i.e, something which is a fake. Hence, the BogoMips value
gives some indication of the processor speed, but it is way too
unscientific to be called anything but BogoMips.

       The reasons (there are two) it is printed during bootup is that
a) it is slightly useful for debugging and for checking that the
computers caches and turbo button work, and b) Linus loves to chuckle
when he sees confused people on the news.'

Cyrix 486-like CPUs need cache enabling software, sometimes referred to
as BogoBoost software. Cyrix 5x86 and 6x86 CPUs may have their BogoMips
improved drastically by branch-prediction (BIOS option). Note that the
performance improvement may be marginal. There are several packages
available for adjusting Cyrix CPUs, such as the bogoboost patch,
cx5x86mod, and set6x86, all from the normal archives, in obvious places.
It is reported the Cyrix 6x86 CPUs may give better performance when the
kernel is compiled with 486-optimization, instead Pentium-optimization.

NexGen 386-enhanced CPUs, marked as Nx586, are listed as 386-like, since
the fact that they are performing like Pentium machines is not relevant
to BogoMips.

AMD 5x86, also denoted as AMD 486DX5, are quadrupled 486/33 machines.
They are fully in line with other 486 CPUs. The AMD K5 and the K6 are
Pentium-like CPUs, with their own BogoMips multipliers.

As a very approximate guide, the BogoMips can be calculated by: 

       System                        BogoMips         Comparison 
       Intel 8088                  clock * 0.004         0.02 
       Intel/AMD 386SX             clock * 0.14          0.8 
       Intel/AMD 386DX             clock * 0.18          1 (definition) 
       Motorola 68030              clock * 0.25          1.4 
       Cyrix/IBM 486               clock * 0.34          1.8 
       Intel Pentium               clock * 0.40          2.2 
       Intel 486                   clock * 0.50          2.8
       AMD 5x86                    clock * 0.50          2.8 
       Mips R4000/R4400            clock * 0.50          2.8
       Nexgen Nx586                clock * 0.75          4.2 
       PowerPC 601                 clock * 0.84          4.7
       Alpha 21064/21064A          clock * 0.99          5.5
       Alpha 21066/21066A          clock * 0.99          5.5 
       Alpha 21164/21164A          clock * 0.99          5.5 
       Intel Pentium Pro           clock * 0.99          5.5 
       Cyrix 5x86/6x86             clock * 1.00          5.6 
       Intel Pentium II            clock * 1.00          5.6
       Intel Celeron               clock * 1.00          5.6
       Mips R4600                  clock * 1.00          5.6 
       Alpha 21264                 clock * 1.99         11.1
       AMD K5/K6/K6-2              clock * 2.00         11.1
       UltraSparc II               clock * 2.00         11.1
       Pentium MMX                 clock * 2.00         11.1 
       PowerPC 604                 clock * 2.00         11.1
       Motorola 68060              clock * 2.01         11.2 

Note that the BogoMips calculation loop does not take full advantage of
the parallelism of various processors, such as the Intel Pentium and the
Alpha 21164. 

Note that the BogoMips calculation loop for the non-Intel CPUs is
similar but not the same.