Subject: Re: timecounters using broken TSC - PC-engines WRAP time problem
To: None <tech-kern@NetBSD.org>
From: Joerg Sonnenberger <email@example.com>
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.