On Sunday, 9 of March 2008, 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. > > 3. Low speed USB devices > > Related, the noise goes away if I insert a USB mouse (low speed). > A high-speed device does not effect the noise, neither does the two built-in > low speed devices (a fingerprint reader and a bluetooth host). > > 4. Battery and AC > > The noise increases with the battery present and also when the AC supply is > removed. > > 5. Second core > > Disabling the second core makes the noise go away. This might be > a subset of 1., as I've been told that a stopped core enters C1. > > > Changing HZ and NO_HZ has no noticeable effect on the problem (except > the odd behaviour in 2.). This is further supported by the fact that Windows > also has the problem (which should behave close to 100 HZ without NO_HZ). > > > So for now, the only viable workaround is processor.max_cstate.... Well, there may be some users willing to trade some battery life for having a quiet box. :-) Perhaps it's worth documenting? Thanks, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
