Message-ID: <5036ED97.8040306@redhat.com>
Date: Thu, 23 Aug 2012 22:57:27 -0400
From: Rik van Riel <riel@redhat.com>
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To: Arjan van de Ven <arjan@linux.intel.com>
CC: linux-kernel@vger.kernel.org, "Rafael J. Wysocki" <rjw@sisk.pl>,
        ShuoX Liu <shuox.liu@intel.com>, mjg59@srcf.ucam.org,
        Boris Ostrovsky <boris.ostrovsky@amd.com>,
        Len Brown <len.brown@intel.com>,
        Deepthi Dharwar <deepthi@linux.vnet.ibm.com>
Subject: Re: [RFC][PATCH 0/3] c-state governor changes
References: <20120823171104.38574add@cuia.bos.redhat.com> <5036A67D.9090904@linux.intel.com>
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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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