Date: Thu, 17 Jan 2008 00:41:26 +1100 (EST) From: Ian Smith <smithi@nimnet.asn.au> To: Tijl Coosemans <tijl@ulyssis.org> Cc: freebsd-acpi@freebsd.org Subject: Re: choice of absolute / relative freqs with est + p4tcc Message-ID: <Pine.BSF.3.96.1080116235819.16926A-100000@gaia.nimnet.asn.au> In-Reply-To: <200801161253.23421.tijl@ulyssis.org>
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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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