High Pitched Whine

[Paul Lipps]

Hello,

I am fairly new to FreeBSD (5.4 was my first version) and I have ran  
into an issue that I think is related to the SMP capabilities of  
FreeBSD. I apologize in advance if this topic is inappropriate for  
this mailing list.

When I am running FreeBSD, my computer emits a high pitched whining  
noise. It's not a 'physical' noise like a fan or hard disk grinding,  
it's more of a electrical whine. It's driving me nuts though, it's  
like a dog whistle. This does not happen when I run any versions of  
Windows or Linux. This has been the case for all versions of FreeBSD  
I have had installed, 5.4, 6.0, and 6.1.

I recently discovered when I do:

sysctl machdep.cpu_idle_hlt=0

the high pitch whine stops.

I have a P4 with HyperThreading, and FreeBSD 6.1 installed a SMP  
kernel by default. I built a non-SMP kernel, and the high pitch whine  
is still there.

So I did a:

sysctl machdep.cpu_idle_hlt=0

after installing the non-SMP kernel and again the whine stopped.

I tried disabling HTT in the BIOS under both the SMP and the non-SMP  
kernel and the whine remained. So regardless if HTT is enabled in the  
BIOS or not, and regardless if I'm running an SMP kernel or not, the  
only thing that gets rid of the high pitch whine is:

sysctl machdep.cpu_idle_hlt=0

Now there is another problem. When I do the command above, the CPU  
temperature rises rapidly. I can tell as my cooling system has a auto- 
throttling fan (Shuttle XPC) and I hear the fan increase in speed  
quickly and steadily after I 'unhalt' the 2nd logical CPU. So the 2nd  
logical CPU must be getting stuck in a loop or something, I'm not  
sure really how to see what is happening.

If anyone has any suggestions as to how this issue could be resolved,  
or could point me in the right direction, I would appreciate it. I  
would be happy to provide dmesg or any other information if it would  
be helpful.

Thank You for your time,

Paul Lipps
paul.lipps at gmail.com