Re: [RFC][PATCH 0/3] c-state governor changes

[Rik van Riel]

On 08/23/2012 05:54 PM, Arjan van de Ven wrote:
> On 8/23/2012 2:11 PM, Rik van Riel wrote:
> > This patch set is mostly there to kick off a discussion in time
> > for Kernel Summit.  When running it on my laptop, with acpi_idle,
> > I see a promising change in powertop.
>
> be careful with acpi_idle... that will remove most of the intermediate C states the platform has,
> so the policy engine no longer has good things to chose from.

Interesting, I was not aware of that.

Another thing I did see is that the intel_idle driver selects
a target residency time around 4x larger than the exit latency
for most c-states, while acpi_idle sticks to 2x by default.

Aiming for a residency time only 2x the exit latency seems
excessively aggressive, especially for the deeper c states.

The latency issues with various KVM guests communicating with
each other have been observed on various Intel and AMD chipsets,
not unique to one vendor.

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