Messages in this thread | | | Date | Thu, 29 Aug 2002 11:02:57 +0100 | From | Padraig Brady <> | Subject | Re: [PATCH][2.5.32] CPU frequency and voltage scaling (0/4) |
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Linus Torvalds wrote: > On 29 Aug 2002, Alan Cox wrote: > >>So what you are saying is that you want to be sure that something like >>"please run at a low speed to save battery" is translated by smarter >>cpus into "please save battery" and on spudstop the CPU would go "umm >>duh ok 300MHz" > > > Yup, exactly. > > I suspect that this is also what most people actually want to use anyway: > you don't care that your CPU is a speedstep 1GHz/500Mhz or a 700/300 (or > whatever the combinations are), you really want to just say "go to power > save mode" vs "go to performance mode". > > Sure, for speedstep, you can obviously trivially _emulate_ this in user > mode with the frequency approach, but for the generic case it isn't. > > I don't know how many policies would be needed (too many just adds > complexity for no gain), but I _suspect_ that something like a > > { min-Hz, max-Hz, policy } > > triple with "policy" being just a few different values ("performance", > "powersave") is sufficient. Clearly this triple trivially _becomes_ the > "single MHz" by just making min and max be the same if you really want one > particular MHz (at which time "policy" doesn't matter). > > With something like the above, you could do something like > > { 0, ~0UL, "performance" } => generic highest performance setting > { 0, ~0UL, "power-save" } => generic power-save setting > { 300, 500, "performance" } => give me a performance setting in the specified range > { 1700, 1700, "performance" } => run at a fixed 1.7GHz
I would go for a quadruple:
{ 0, ~0UL, 0, "performance" } => generic highest performance setting { 0, ~0UL, 0, "power-save" } => generic power-save setting { 300, 500, 0, "performance" } => give me a performance setting in the { 1700, 1700, 70"performance" } => run at a fixed 1.7GHz { 0, ~0UL, 70, "performance" } => performance but don't go above 70°C
would you also want a hysteris value?
Pádraig.
> (maybe the "policy" thing actually makes a difference even for the > fixed-frequency case: it can give hints about whether to allow C1-C3 > states when idle etc). > > Linus
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