Subject: Re: timecounters using broken TSC - PC-engines WRAP time problem
To: None <>
From: Joerg Sonnenberger <>
List: tech-kern
Date: 11/29/2007 15:04:20
On Thu, Nov 29, 2007 at 03:24:19PM +0100, theo borm wrote:
> It mentions VMware, and my /guess/ was that timecounters can get confused 
> when the TSC is modified outside the netbsd scope (and that would suggest 
> potential problems with XEN too).

Most modern systems just use the ACPI timer, which has a higher priority
and is typically a lot more stable.

>> Does your system have an AMD Geode SC1100 or similiar? I found a
>> discussion for Linux that mentioned that the TSC is broken as it is not
>> incremented during halt.
> Yes. The fact that the TSC is broken is also mentioned in the dmsg, but 
> despite this it /is/ used.

Can you try boot -d and "w tsc_is_broken=1"?

> I'm wondering if using the TSC rather than the i8254 by default is such a 
> good idea. It may be more accurate than the i8254 /when/ it is working, but 
> if the i8254 clock is more reliable, I would prefer that.

It is not so much a question of accuracy, but rather that the i8254
timer is extremely slow on most systems.