Natty SRU: x86, intel, power: Initialize MSR_IA32_ENERGY_PERF_BIAS

Seth Forshee seth.forshee at
Tue Sep 20 19:45:48 UTC 2011

On Tue, Sep 20, 2011 at 11:29:31AM -0600, Tim Gardner wrote:
> From 6e243f86d1424d7a1d67da4f8527239a786d9c2f Mon Sep 17 00:00:00 2001
> From: Len Brown <len.brown at>
> Date: Thu, 14 Jul 2011 00:53:24 -0400
> Subject: [PATCH] x86, intel, power: Initialize MSR_IA32_ENERGY_PERF_BIAS
> BugLink:
> commit abe48b108247e9b90b4c6739662a2e5c765ed114 upstream.
> Since 2.6.36 (23016bf0d25), Linux prints the existence of "epb" in /proc/cpuinfo,
> Since 2.6.38 (d5532ee7b40), the x86_energy_perf_policy(8) utility has
> been available in-tree to update MSR_IA32_ENERGY_PERF_BIAS.
> However, the typical BIOS fails to initialize the MSR, presumably
> because this is handled by high-volume shrink-wrap operating systems...
> Linux distros, on the other hand, do not yet invoke x86_energy_perf_policy(8).
> As a result, WSM-EP, SNB, and later hardware from Intel will run in its
> default hardware power-on state (performance), which assumes that users
> care for performance at all costs and not for energy efficiency.
> While that is fine for performance benchmarks, the hardware's intended default
> operating point is "normal" mode...
> Initialize the MSR to the "normal" by default during kernel boot.
> x86_energy_perf_policy(8) is available to change the default after boot,
> should the user have a different preference.
> Signed-off-by: Len Brown <len.brown at>
> Link:
> Acked-by: Rafael J. Wysocki <rjw at>
> Signed-off-by: H. Peter Anvin <hpa at>
> Signed-off-by: Greg Kroah-Hartman <gregkh at>
> Signed-off-by: Tim Gardner <tim.gardner at>

SRU justification is missing on the bug.

Acked-by: Seth Forshee <seth.forshee at>

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