Re: [PATCH] 3/3 Dynamic cpufreq governor and updates to ACPIP-state driver

[Dominik Brodowski <linux@brodo.de>]

On Tue, Oct 21, 2003 at 12:55:55PM -0700, Carl Thompson wrote:
> Quoting "Nakajima, Jun" <jun.nakajima@intel.com>:
> 
> > ...
> 
> > It's about the frequency of the feedback loop. As we have much lower
> > latency with P-state transitions, the sampling time can be order of
> > millisecond (or shorter if meaningful). A userland daemon can have a
> > high-level policy (preferences, or set of parameters), but it cannot be
> > part of the real feedback loop. If we combine P-state transitions and
> > deeper C-state transitions, the situation is worse with a userland
> > daemon.
> 
> You are making the assumption that a higher polling frequency (we'll say
> 1ms) is in general better than a lower frequency (we'll say 1s).  I submit
> that it is not.
> 
> If I hit a key on my keyboard and your high frequency loop increases CPU
> speed so that my word processor displays the letter 0.01s faster, is that
> really beneficial?  If a window renders in 0.2s seconds instead of 0.3s is
> that a difference I am going to notice?
> 
> On the other hand, if I do a kernel compile and it is done 0.999s faster
> with the higher frequency loop, am I going to miss that second over such a
> long duration?  (In reality, the compile with the high-frequency loop would
> probably take longer unless it has near zero overhead).
> 
> In my opinion it is wasteful to increase CPU speed unless there is a longer
> term need for it.

Different needs, different opinions, different governors...

	Dominik