[linux-audio-user] CPU clock - beware

tim hall tech at glastonburymusic.org.uk
Sat Jul 24 22:13:37 EDT 2004

Last Saturday 24 July 2004 15:12, Stefan Scheffler was like:
> hmm ... are you sure about the type of processor? AFAIK only Celerons
> +700 mhz support a 100mz fsb.

I'm just reading the motherboard manual.

> Intel has a utility to check cpu information bus speed and so on ..
> sadly it's windows/dos only:
> http://downloadfinder.intel.com/scripts-df/Product_Filter.asp?ProductID=441

Won't be much use to me then ;-)

Thanks for the other suggestions tho'

> >I think it's probably more a question of me explaining badly. I think I've
> >just set it to the maximum I can get with this mobo & processor. The one
> >weirdness is that the processor is now being detected as 900MHz, which is
> > not true. Perhaps the 1800 bogomips reading is, I don't know.
> now that is uh  ... interesting  ... so within two days you like almost
> quadrupled your processor speed .. congratulations :D

Yeah, basically I suspect I've been driving with the handbrake on :-]

> could you post the output of "cat /proc/cpuinfo"? I'd love to see that. :)

~$ cat /proc/cpuinfo
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 8
model name      : Celeron (Coppermine)
stepping        : 6
cpu MHz         : 896.977
cache size      : 128 KB
fdiv_bug        : no
hlt_bug         : yes
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 2
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca 
cmov pat pse36 mmx fxsr sse
bogomips        : 1789.13

> just FYI:
> "model name      :" should tell you the name and aometimes the design
> speed of the cpu
> "cpu MHz" the real current speed
> "bogomips" issome weird timing value I have no idea what it means exactly
It's a semi-arbitrary benchmarking value, usually twice the processor speed. 

Last Saturday 24 July 2004 16:33, Matthew Barber was like:
> Be careful doing something like that, especially with old boards.  I
> think setting the fsb clock to "no man's land" will set the pci clock
> (and AGP if you have AGP on your board) to something unusable, unless
> BIOS locks the PCI/AGP clock to a certain range of values.  PCI
> generally wants to run at about 33Mhz (unless you have a very new board
> with PCI-X or some such), and AGP at 66Mhz, and these values will
> generally be a fraction of the fsb.  So if your fsb is 66Mhz, PCI will
> be 1/2FSB.  If it's 100Mhz, PCI will be 1/3.  Setting it to 75Mhz may
> cause it to still be in the 66Mhz realm as far as the division is
> concerned, and set PCI to around 38Mhz, which may cause a lot of
> problems.  I know some BIOS will take care of this by locking AGP and
> PCI to a certain value, but I wouldn't count on it with an older
> board/bios.

This is what I guessed, I'm using the values specified in the manual for a 
Coppermine FC-PGA 600, so:
at 3x clock ratio I get:
CPU (I assume this is FSB) 100
PCI 33
AGP 66
The display cache runs at 100MHz too, a 1:1 ratio seems logical.
One of the reasons I only have 192MB of RAM is because I have already been 
fussy enough only to use memory that is supposed to run at 100MHz too.
No-man's land FSBs are only relevant if overclocking, which is not the object 
of the exercise for me. I'm trying to optimise.

I don't think I'm doing _too_ badly.

Last Saturday 24 July 2004 17:49, Ryan Underwood was like:
> Where?  Is there an online copy of this manual?

I found one here:

I think I might read it now. I'm a bit confused as to why my system thinks 
it's running a 896MHz CPU, But so far there's no overt signs that it isn't 
happy, so I'll prod it a bit and see ;-)


tim hall

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