[Xen-users] Kernel config guidelines for xen power management

[Matthias <matthias.kannenberg@xxxxxxxxxxxxxx>]

Because most of the documentation on xen power managmeent is largely outdated or not that specific, I wanted to ask around if there are some general guidelines on what to use kernel wise to let the xen power managment work as best as possible.

As far as I understand the general prospect is that the xen sceduling / cpuidle should replace the cpuidle function of the kernel when booted with xen support because xen has general a better understanding of the actual load on the system because it can judge domU load better then the kernel would be able to.

But I would guess that the kernel itself needs to be configured a certain way for this to work. Especially with things like ticks vs. dynticks vs. tickless idle and irq time accounting, I would assume that these are not all equally supported by Xen.

I know that kernel configs are different for every system / user, but I thing there should be some common best practices and general "Don't use xyz because it is known to cause issues".

Scrolling through my kernel, I thing these options might be important, but feel free to add additional things:

Â> General setup > Timers subsystem (no dynticks, tickless idle, tickless) and resulting options
Â> General setup > CPU/Task time and stats accounting (simple tick based, full dynticks, IRQ time accounting) and resulting options
Â> General setup > RCU Subsystem (any special options here, like RCU priority boosting etc)
ÂAutomatic process group scheduling (CONFIG_SCHED_AUTOGROUP) y/n
Â> Enable the block layer > IO Schedulers (anythig else then * everything and CFQ scheduler?)
Â> Processor type and features > Preemption Model (server, desktop, low latency desktop)
Â> Processor type and features > Timer frequency
Â> Power management and ACPI options > CPU Frequency scaling (basically everything here)
CONFIG_ACPI_PROCESSOR must be * ?
Â> Power management and ACPI options > ACPI (Advanced Configuration and Power Interface) Support (anything else specifig here?)

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