[clue-tech] 2.6 kernel compile options make Intel CPU slow

[Maxwell Spangler]

On Wed, 2010-08-04 at 14:31 -0600, Jim Ockers wrote:

> The problem is that when the cooling fails (failed fan or clogged heat
> sink), we get a significant performance hit, so we need to know right
> away if that happens and we don't always get good information about
> the cooling.  The thing we see right away is slow system performance
> but it manifests itself in a variety of weird and non-obvious ways.
> We have determined that we need maximum performance and nothing less
> is OK so we were trying to detect failures right away.
> > So you can use a 2.4 kernel for cooling measurements.
> >   
> A 2.6 kernel with SMP turned off behaves the same, scheduler-wise, as
> the 2.4 kernel (and I'm sure that was not a SMP kernel either) on the
> hyperthreading P4.
> > Can you measure/detect CPU temperature (which ought to relate somehow to throttling)?
> >   
> Yes but not reliably enough in our 2004-vintage hardware.
> > Can you measure power consumption (which ought to decrease when throttling)?
> >   
> Good idea, but unfortunately no in our old hardware.

Is this proprietary hardware or some old 2004 era x86 PC motherboard?

If it's the latter I would think you could probe for the CPU speed and
use that (assuming that high temperatures means lowered Mhz speed equals
poor performance?).

I'm still really curious about your dd issue.

dd if=/dev/zero of=/dev/null

in my mind is

1) execute the dd command which simply reads in one channel and outputs
to another
2) the input channel of /dev/zero should be so simple and fast that it
can push a CPU at full speed (no i/o wait on calculating zeros, etc)
3) the output channel of /dev/null should be so simple and fast that it
can push a CPU at full speed (no i/o wait on writes, etc)

So why does a command that should be so simple take a performance hit in
a hyperthreading environment?  It bothers me, although I'm sure not as
much as you.

-- 
Maxwell Spangler
========================================================================
        Linux, Unix and Database Administration
        Currently: Boulder, Colorado
        LinkedIn: http://www.linkedin.com/in/maxwellspangler