[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-users] Does Xen's Dom0 hypervisor based cpufreq support 'schedutil' governor?

  • To: xen-users@xxxxxxxxxxxxx
  • From: "Austin S. Hemmelgarn" <ahferroin7@xxxxxxxxx>
  • Date: Tue, 23 Aug 2016 14:15:49 -0400
  • Delivery-date: Tue, 23 Aug 2016 18:16:11 +0000
  • List-id: Xen user discussion <xen-users.lists.xen.org>

On 2016-08-23 13:52, lists@xxxxxxxxxxxx wrote:
I use Xen 4.7.0_10 on Linux kernel 4.7.2

I set/use Xen's Hypervisor based cpufreq, setting


Kernel 4.7.2 supports 'schedutil' governor. 

From the xenpm manpage, you can set the governor to

        set-scaling-governor  [cpuid] <gov> set scaling governor on CPU <cpuid> 
or all as userspace/performance/powersave/ondemand

but NOT 'schedutil'.

Does Xen support using the kernel's 'schedutil'?  How's it configured?

I'm not 100% certain that I've ever completely understood cpufreq in Xen, but it's been my understanding that the xenpm set-scaling-governor command is used to set what governor Xen uses when cpufreq=xen is specified on the command line. This does not use Linux's cpufreq governors or drivers at all. To do that, you need to:
1. Set cpufreq=dom0 on the Xen command line.
2. Give Domain-0 a number of VCPU's exactly equal to the number of physical CPU's.
3. Pin Domain-0's VCPU's to PCPU's.
4. Possibly have some special support in Domain-0 (I'm not certain about this).

Assuming that I understand how this all works correctly, any Linux governor should work, but schedutil would make no sense since it interfaces with Linux's scheduler, not Xen's, which means it will be basing it's decisions on information that has nothing to do with actual load. In general, there's very little practical use to having Domain-0 set CPU frequency, as you can just as easily use xenpm from a separate daemon which monitors the relevant data to set the frequencies as you want.

Xen-users mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.