[tlinux-users:08190] Re: toshset -cpu fast/slow, what mHz?

On Wed, Sep 20, 2006 at 04:46:08PM -0500, Ryan Underwood wrote:
> 
> Hello,
> 
> When the SCI interface is used to set the CPU speed "fast" or "slow",
> what speed is the "slow" speed of the CPU?  Is it half speed or
> something else?  The system is noticeably slower, but x86info -mhz still
> returns the original MHz rating.

It appears that on a Tecra 500CDT, the "slow" speed is accomplished via
SMI throttling.  I observed that the TSC rate did not slow down when the
processor was slowed.  Then after discussing this, someone on the
cpufreq list pointed out this patent, which seems to be precisely what
Toshiba implemented on this laptop:
http://www.freepatentsonline.com/7082542.html

Unfortunately, that means the "slow" mode of the processor saves no more
power than Linux already does, because the SMI handler (invoked by
laptop's core logic) executes HLT when throttling, just like Linux's
idle loop.  It additionally adds latency due to SMI round trips (at
around 800K cycles apiece) that Linux would not have.

Too bad!

-- 
Ryan Underwood, <[email protected]>