Re: [RFC PATCH] x86:Use cpu_khz for loops_per_jiffy calculation

Arjan van de Ven
2008-06-04T01:20:28Z

On Tue, 03 Jun 2008 17:41:09 -0700
Alok Kataria <akataria@vmware.com> wrote:

> On X86 platform we can use the value of cpu_khz computed during tsc
> calibration to calculate the loops_per_jiffy value. Its very
> important to keep the error in lpj values to minimum as any error in
> that may result in kernel panic in check_timer.
> In virtualization environment on a highly overloaded host, the guest
> delay calibration may sometimes result in errors beyond the ~50% that
> timer_irq_works can handle, resulting in the guest panicking.
\

can you guarantee that the rate tsc ticks at is the same as the current
CPU frequency? Answer: You can't....

sadly we do need to calibrate this...

In addition, clearly you can have different cpus in a system run at a
different rate (both in terms of cpu_khz and, independently, in terms
of tsc rate)

--
If you want to reach me at my work email, use arjan@linux.intel.com
For development, discussion and tips for power savings,
visit http://www.lesswatts.org