[Xen-users] Question about Xen cpufreq and scheduling.

[Austin S Hemmelgarn <ahferroin7@xxxxxxxxx>]

Background:
i've got a home server system that I'm using Xen on to isolate specific 
groups of services from each other.  I've got 6 domains beyond dom0, 5 
of them are for network services, and one is used to run a BOINC 
distributed computing client.  Currently, the regular 'credit' scheduler 
is working perfectly for my needs (and doing a much better job than 
Linux's native scheduler at isolating the distributed computing client 
from the network services).  However, the cpufreq drivers (both in Xen 
itself and when using dom0 for controlling the frequency) don't work 
very well for my use case, which brings me to my question.
Question:
Is there any way to tell Xen's cpufreq governors to ignore a single 
domain when calculating what frequency to use.  Everything in the my 
BOINC domain is memory bound, and there's less than a 2.5% performance 
difference on my hardware between running it at 1.4GHz and 3.2GHz. 
Based on this, I'd really like to be able to have the cpufreq governor 
ignore that domain when computing how loaded the system is, but still 
scale up the frequency when the other domains are busy with something.
On Linux there is an option for the 'ondemand' cpufreq governor to tell 
it to ignore low-priority tasks and/or stuff waiting on I/O completion 
when setting the frequency.  Looking through the documentation for Xen, 
I've been unable to find anything remotely equivalent to this.
If such functionality doesn't exist, how hard would it be to actually 
add it?  I would think that this type of usage would likely be 
non-existent for people using the realtime schedulers, and for credit 
and credit2 it would make sense to just provide some user-configurable 
scheduling weight below which domains would get ignored by cpufreq.

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