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

  • To: xen-users <xen-users@xxxxxxxxxxxxx>
  • From: Austin S Hemmelgarn <ahferroin7@xxxxxxxxx>
  • Date: Wed, 28 Oct 2015 11:29:50 -0400
  • Delivery-date: Wed, 28 Oct 2015 15:31:12 +0000
  • List-id: Xen user discussion <xen-users.lists.xen.org>

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.

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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