bogomips

[Tim Seufert]

On Sunday, December 1, 2002, at 04:00  AM, Eddie Bindt wrote:

> On 1 Dec 2002, Owen Stampflee wrote:
>>
>>> Bogomips = MHz * 2 for all PPC procesors
>> Not true...
>>
>> [owen@fred owen]$ cat /proc/cpuinfo
>> cpu             : 603ev
>> clock           : 200MHz
>> revision        : 2.1 (pvr 0007 0201)
>> bogomips        : 133.12
> this is because you probably booted this machine with a not-so-good
> version of bootx ... There where endless discussions about this 
> problem in
> the mailinglists ages ago. Get the right booter and you will see the
> machine getting faster ...

[snip results for 604 boxen]

> So, in general, 2*cpuclock should be OK ...

No, 2*clock is expected only on some PPC CPUs.  Specifically, the 604 
family, 750 (G3) family, and 7400 (G4) family.  The ratio Owen reported 
above is perfectly normal for a 603e and does not indicate he has the 
bootx problem.  If he did, it would be much worse than 200:133.

Bogomips is nothing more than a very tight timing loop.  In most (all?) 
PPC Linux kernels the loop is a single bdnz (branch and decrement if 
nonzero) instruction.  If you get 2 * MHz Bogomips scores, that means 
your CPU can execute two bdnz instructions per cycle.  Not all PPCs can 
do that.