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

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Date:	Thu, 23 Aug 2012 22:57:27 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Arjan van de Ven <arjan@...ux.intel.com>
CC:	linux-kernel@...r.kernel.org, "Rafael J. Wysocki" <rjw@...k.pl>,
	ShuoX Liu <shuox.liu@...el.com>, mjg59@...f.ucam.org,
	Boris Ostrovsky <boris.ostrovsky@....com>,
	Len Brown <len.brown@...el.com>,
	Deepthi Dharwar <deepthi@...ux.vnet.ibm.com>
Subject: Re: [RFC][PATCH 0/3] c-state governor changes

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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