Re: [Xen-devel] [PATCH] Disable Xen PowerNow! support on Opteron 2nd gen and earlier processors

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 25/1/08 22:58, "Mark Langsdorf" <mark.langsdorf@xxxxxxx> wrote:

> I tried this suggestion and also implemented the trace function in
> cpu_frequency_change() and local_time_calibration() you suggested in
> a previous message.
> 
> It made no discernable difference in my tests.  I did high to low
> and low to high changes roughly every five minutes, and always got
> an excessive difference inside of Xen and usually got error messages
> in Linux.

It's a bit confusing as to what is going on since there are 4 CPUs in the
system. Are arbitrary or all CPUs changing frequency, or just one of them?
Is the single-step PSTATE_CTRL MSR being used, or the multi-step FID_VID
method where voltage adjustments are under software control? What is the
system's CPU topology, and do any of the cores have their frequency controls
tied together?

It'd be useful to have each tracing line stamped with the CPU that it comes
from. As it is the tracing looks very suspect because the systimes on
adjacent lines are much less than one second, and calibration is supposed to
happen no more than once per second.

 -- Keir



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