Re: [PATCH] x86: intel_epb: Do not build when CONFIG_PM is unset

[Ingo Molnar <mingo@kernel.org>]

* Rafael J. Wysocki <rjw@rjwysocki.net> wrote:

> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> Commit 9ed0985332a6 ("x86: intel_epb: Take CONFIG_PM into account")
> prevented the majority of the Performance and Energy Bias Hint (EPB)
> handling code from being built when CONFIG_PM is unset to fix a
> regression introduced by commit b9c273babce7 ("PM / arch: x86:
> MSR_IA32_ENERGY_PERF_BIAS sysfs interface").
> 
> In hindsight, however, it would be better to skip all of the EPB
> handling code for CONFIG_PM unset as there really is no reason for
> it to be there in that case.  Namely, if the EPB is not touched
> by the kernel at all with CONFIG_PM unset, there is no need to
> worry about modifying the EPB inadvertently on CPU online and since
> the system will not suspend or hibernate then, there is no need to
> worry about possible modifications of the EPB by the platform
> firmware during system-wide PM transitions.
> 
> For this reason, revert the changes made by commit 9ed0985332a6
> and only allow intel_epb.o to be built when CONFIG_PM is set.
> 
> Note that this changes the behavior of the kernels built with
> CONFIG_PM unset as they will not modify the EPB on boot if it is
> zero initially any more, so it is not a fix strictly speaking, but
> users building their kernels with CONFIG_PM unset really should not
> expect them to take energy efficiency into account.  Moreover, if
> CONFIG_PM is unset for performance reasons, leaving EPB as set
> initially by the platform firmware will actually be consistent
> with the user's expectations.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
> 
> This is complementary to the EPB handling changes made in the current
> development cycle, so IMO it would be good to do it in this cycle too
> if there are no technical concerns or objections regarding it.

Sure:

Acked-by: Ingo Molnar <mingo@kernel.org>

Thanks,

	Ingo