1kHz noise from C3 sleep

[Nate Lawson]

Alexander Leidinger wrote:
> Nate Lawson <nate at root.org> wrote:
> 
> [Moving to -current]
> 
>>> I wonder if moving to HZ=1000 on amd64 and i386 was really all that good
>>> of an idea.  Having preemption in the kernel means that ithreads can run
>>> right away instead of having to wait for a tick, and various fixes to
>>> 4BSD in the past year have eliminated bugs that would make the CPU wait
>>> for up to a tick to schedule a thread.  So all we're getting now is a
>>> 10x increase in scheduler overhead, including reading the timecounters.
>>
>>
>> I use hz=100 on my systems due to the 1 khz noise from C3 sleep. 
>> Windows has the same problem.
> 
> 
> My laptop makes noises when being (more or less) idle (I think I enabled
> C3...). Does this mean I should try to change HZ?

Sure, you can do it from a tunable (kern.hz I think), you don't have to 
recompile.

> If yes: Windows doesn't make such a noise, does this mean it doesn't use C3
> on this system (your comment suggests that Windows does use a HZ=1000 like
> behavior)?

It's possible it doesn't.  Windows 2000 and newer uses hz=1000.

-- 
Nate