cpuinfo wrong report ?

[Vu Pham]

On Tue, 2007-01-30 at 10:25 -0500, David Bandel wrote:
> On 1/30/07, Vu Pham <vu at sivell.com> wrote:
> > I am playing some settings of the new motherboard.
> >
> > When I change the clock multiplier, /proc/cpuinfo does show the change
> > of CPU Mhz accordingly and shows the same value that the motherboard
> > shows ( 3.2Ghz )
> >
> > But when I change ( increase ) the host clock, the cpuinfo shows the cpu
> > mhz dropped dramtically : 600 Mhz ( less than 1Ghz ) instead of 3.54
> > Ghz.
> >
> > In both cases, the bpgomips values increase as expected.
> >
> > Is it a bug ?
> 
> Is it a bug that apples and oranges taste different?

David, I thought when the physical CPU speed increases then the tool
will show that increase, not decrease. In this case, it does show the
increase when the CPU speed  increases by the multiplier, and decrease
when the CPU speed increases by the host clock. In both cases, the CPU
speed does increase, why it shows different results ? I am sure that I
am missing something here, so any explanation is really appreciated.


> > The second question: this Intel CPU will run at lower clock  ( 1.6 Ghz )
> > when there is little load and moves to a higher (3.2Ghz) when there is
> > more load. Is there any kernel settings that can keep the cpu always at
> > high frequency clock ?
> 
> Why, when the CPU is idle (over 80% of the time) would you want to run
> it hotter?

No, I do not want it to run hotter. As you see, I use cpuinfo to check
the  physical cpu speed. When the cpu is not in the high-load mode,
cpuinfo shows me the lower speed, and I do not know if it is the speed
for the low load or high load.

> Besides, do you know that Linux (but not all OS's) sends the the Halt
> command to the CPU?  Perhaps you'd like to kill that too?
> 
> Stepping the processor down and halting it while it's not working
> extends the CPU life, reduces power consumption, but does not hurt
> performance. 
> Why do you:
> a.  insist on overclocking rather than just buying a faster board and processor?
> b.  want to defeat mechanisms that don't hurt performance?

In general I do not need to overclock my systems and when I need
something faster, I often try some faster board and processor, if I ( or
my company ) can afford. 

In this particular case, I have to finish my project in a pretty short
time, and the tool I am using runs pretty slow in debugging mode. It
seems the system bottleneck is the cpu and I already got the fatest cpu
( X6800) for my workstation ( I may be wrong, as I often am ). Just hope
the CPU does not die before I finish the project :). 

In fact, Google shows many people overclock it up to 4 Ghz and I only
try to 3.5Ghz. Perhaps I am not so mean as them. :)


> If you want to destroy your CPU, a hammer will do it faster and you
> won't have to worry about errors, random lockups that have no apparent
> cause, etc., as the system dies a tortured death.

I did, not by hammer, but by sweat. About 20 years ago I was working on
an Apple II installing my ADC board, my sweat ( no AC where I
practiced ) dropped onto the pins of the chip 6502, IIRC, and I had to
spend almost my salary to buy that chip back.

Thanks for your reply,

Vu