Re: Xen cpufreq support status: how to notify hypervisor of frequency change?

["Matt T. Yourst" <yourst@yourst.com>]

On Tuesday 11 April 2006 04:25 am, Keir Fraser wrote:
>
> All this stuff should be done by emulating the MSR writes in
> emulate_privileged_op() in arch/x86/traps.c. This will avoid any
> modification of Linux at all. Currently there's only simple filtering
> of MSR write attempts, but picking up on cpu-freq MSR accesses on e.g.,
> AMD systems and also resync'ing the local clock would not be difficult.
>

I'll give this a try - it should be much cleaner than my current method and 
may avoid some race issues (see below).

We may need to duplicate some work done by the dom0 kernel and read out the 
frequency/voltage tables, since the MSR write on AMD chips (and probably 
Intel) does not specify an actual "XXX MHz" number - it's just an index into 
the FID/VID table. I'll investigate this, but I need someone with an Intel 
chip to do the same, since I have no way of testing those MSRs.

I'm still getting some issues with the timer not properly re-syncing even 
though the cpufreq driver makes the new setcpufreq hypercall, which Xen 
properly receives.

Right now it just sets cpu_khz and calls local_time_calibration() on the 
target CPU(s). Is there something else we need to do, like calling the 
equivalent of early_time_init() or init_xen_time() all over again?

The problem is much less severe now but it still sometimes happens.

- Matt

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 Matt T. Yourst               yourst@cs.binghamton.edu
 Binghamton University, Department of Computer Science
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