choice of absolute / relative freqs with est + p4tcc
Ian Smith
smithi at nimnet.asn.au
Wed Jan 16 05:41:37 PST 2008
On Wed, 16 Jan 2008, Tijl Coosemans wrote:
> On Wednesday 16 January 2008 05:29:47 Ian Smith wrote:
[..]
> > dev.cpu.0.freq_levels: 1200/-1 1100/-1 1000/-1 900/-1 800/-1 700/-1 600/-1 525/-1 450/-1 375/-1 300/-1 225/-1 150/-1 75/-1
> > dev.est.0.freq_settings: 1200/-1 1100/-1 1000/-1 900/-1 800/-1 600/-1
> > dev.p4tcc.0.freq_settings: 10000/-1 8750/-1 7500/-1 6250/-1 5000/-1 3750/-1 2500/-1 1250/-1
> >
> > .. and find myself curious why 550 (1100 * .5) and 500 (1000 * .5)
> > would not be chosen when 525 (600 * .875) was, going by the comments:
> >
> > /*
> > * Walk the set of all existing levels in reverse. This is so we
> > * create derived states from the lowest absolute settings first
> > * and discard duplicates created from higher absolute settings.
> > * For instance, a level of 50 Mhz derived from 100 Mhz + 50% is
> > * preferable to 200 Mhz + 25% because absolute settings are more
> > * efficient since they often change the voltage as well.
> > */
> > and
> > /*
> > * Insert the new level in sorted order. If it is a duplicate of an
> > * existing level (1) or has an absolute setting higher than the
> > * existing level (2), do not add it. We can do this since any such
> > * level is guaranteed use less power. For example (1), a level with
> > * one absolute setting of 800 Mhz uses less power than one composed
> > * of an absolute setting of 1600 Mhz and a relative setting at 50%.
> > * Also for example (2), a level of 800 Mhz/75% is preferable to
> > * 1600 Mhz/25% even though the latter has a lower total frequency.
> > */
>
> It's because of (2) in the second comment. 550 and 500 likely use more
> power than 600 and 525, so it doesn't make sense to use them.
Ah, ok, thanks.
I hadn't really grokked (2) as it compares 600 with 400MHz, which seemed
'obviously' preferable, but for the wrong reason .. pardon the noise.
cheers, Ian
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