Re: [tlug] CPU speed: reported vs. actual

[Attila Kinali <attila@example.com>]

On Thu, 14 Jul 2011 11:29:42 +0900
Darren Cook <darren@example.com> wrote:

> Any thoughts as to how I confirm this, and get it running at full-speed?
> (Ubuntu 10.04, 64 bit, linux 2.6.32)

I would rather ask whether you are measuring the thing you want to measure.

Some things to think about:

* What cpufreq governor are you using? Have a look at
  /sys/devices/system/cpu/cpufreq

* Is your system really cpu bound? Is it not I/O bound or memory I/O bound?
  If you can, have a look at the cache hit statistics (don't know what tools
  to use for this)

* It could be that the i7 scales the cpu frequency of a core up independently
  w/o interaction with the OS, depending on how much power is used by the
  other cores. This is called Turbo Boost and is basically an inverse
  frequency scaling.


My guess would be that your application is not really cpu bound, unless
you do some serious number crunching and instead are hiting some other
limit that does not scale together with the cpu frequency. And given 
the complexity of modern cpus, i can assure you, that is very unlikely
that you are using the maximum computation speed of the ALUs, but rather
are hiting some other wall that is of peripheral nature and thus actually
do not even run the cpu at full throttle even if the frequency scalling
is at maximum.

For more information on this, please read the processor manuals provided
by intel... they make a good bed time reading... for the next few months ;-)


			Attila Kinali

-- 
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
		-- Tirin, The Dispossessed, U. Le Guin