Re: [linux-pm] [PATCH] cpuidle: avoid singing capacitors

[Pavel Machek]

On Sun 2008-03-09 15:16:59, Pierre Ossman wrote:
> I'm beginning to think this is a lost cause. I've tried several variants, all without satisfactory results.
> 
> In case anyone else has any more ideas, I'll detail what I've found influences the noise:
> 
> 1. C state
> 
> This is the big one. There is no noise as long as C3 is avoided (processor.max_cstate).
> 
> 2. uhci_hcd driver
> 
> USB is somehow involved in this problem. Unloading the uhci_hcd driver almost entirely kills the noise on a 1000 HZ NO_HZ kernel. On a 100 HZ, no NO_HZ kernel, the effect is very small, but still there.

USB keeps processor out of C3 in many cases.

> 4. Battery and AC
> 
> The noise increases with the battery present and also when the AC supply is removed.
>

On battery, some machines swap C3 for "secret" C4, which is slower but
saves power.
									Pavel
-- 
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