Message-Id: <20101026202307.c028e26c.akpm@linux-foundation.org>
Date:	Tue, 26 Oct 2010 20:23:07 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Len Brown <lenb@...nel.org>
Cc:	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] tools: add x86_energy_perf_policy to program
 MSR_IA32_ENERGY_PERF_BIAS

On Sat, 23 Oct 2010 00:40:18 -0400 (EDT) Len Brown <lenb@...nel.org> wrote:

> MSR_IA32_ENERGY_PERF_BIAS first became available on Westmere Xeon.
> It is implemented in all Sandy Bridge processors -- mobile, desktop and server.
> It is expected to become increasingly important in subsequent generations.
> 
> x86_energy_perf_policy is a user-space utility to set this
> hardware energy vs performance policy hint in the processor.
> Most systems would benefit from "x86_energy_perf_policy normal"
> at system startup, as the hardware default is maximum performance
> at the expense of energy efficiency.  See the comments
> in the source code for more information.
> 
> Linux-2.6.36 added "epb" to /proc/cpuinfo to indicate
> if an x86 processor supports MSR_IA32_ENERGY_PERF_BIAS,
> though the kernel does not actually program the MSR.
> 
> In March, Venkatesh Pallipadi proposed a small driver
> that programmed MSR_IA32_ENERGY_PERF_BIAS, based on
> the cpufreq governor in use.  It also offered
> a boot-time cmdline option to override.
> http://lkml.org/lkml/2010/3/4/457
> But hiding the hardware policy behind the
> governor choice was deemed "kinda icky".
> 
> So in June, I proposed a generic user/kernel API to
> consolidate the power/performance policy trade-off.
> "RFC: /sys/power/policy_preference"
> http://lkml.org/lkml/2010/6/16/399
> That is my preference for implementing this capability,
> but I received no support on the list.
> 
> So in September, I sent x86_energy_perf_policy.c to LKML,
> a user-space utility that scribbles directly to the MSR.
> http://lkml.org/lkml/2010/9/28/246
> 
> Here is the same utility re-sent, this time proposed
> to reside in the kernel tools directory.
> 
> Signed-off-by: Len Brown <len.brown@...el.com>
> ---
>  tools/power/x86/x86_energy_perf_policy/Makefile    |    7 +
>  .../x86_energy_perf_policy.c                       |  358 ++++++++++++++++++++
>  2 files changed, 365 insertions(+), 0 deletions(-)
>  create mode 100644 tools/power/x86/x86_energy_perf_policy/Makefile
>  create mode 100644 tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c

tools/power/x86, eh?  It seems a better place than under
Documentation/, where such things have thus far landed!

I looked briefly, wondering about the kbuild situation.  It doesn't
appear to be wired up, so one has to manually enter that directory and
type `make'?

I guess that's OK as an interim thing but longer-term I suppose we
should have some more complete build and deployment system.  So
(thinking out loud) a `make' would invoke a `make tools', and that
`make tools' would build the tools which are specific to the target
arch[*], and any generic ones.  And a `make tools_install' would install
those tools in, I guess, /lib/modules/$(uname -r)/bin.

Or something else.  We'd need input from the distro guys to get this
right.

[*]: building tools for the `target arch' would require a far more
extensive cross-build environment than is needed for just kernel
cross-compilation.  This is perhaps Just Too Hard and perhaps a `make
tools_install' should copy the *source* into /lib/modules/$(uname
-r)/src and you then finish the build on the target.  Or something
else.  The mind boggles.

So for now, just parking the source down in ./tools/ and deferring the
problem sounds a fine idea ;)

A number of programs down under Documentation/ should be moved into
tools/ as well.

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