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SubjectRe: [linux-pm] [PATCH] cpuidle: avoid singing capacitors
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.
(cesky, pictures)

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