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From: Ingo Molnar <mingo@kernel.org>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: x86 <x86@kernel.org>, Linux PM <linux-pm@vger.kernel.org>,
	Ido Schimmel <idosch@idosch.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Len Brown <len.brown@intel.com>,
	Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	Laura Abbott <labbott@fedoraproject.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Simon Schricker <sschricker@suse.de>,
	Borislav Petkov <bp@suse.de>, Hannes Reinecke <hare@suse.de>
Subject: Re: [PATCH] x86: intel_epb: Do not build when CONFIG_PM is unset
Date: Thu, 30 May 2019 09:47:10 +0200	[thread overview]
Message-ID: <20190530074710.GA68696@gmail.com> (raw)
In-Reply-To: <3844875.YPkTDDlcrF@kreacher>


* 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

      reply	other threads:[~2019-05-30  7:47 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-21 22:12 [PATCH 0/2] PM / arch: x86: MSR_IA32_ENERGY_PERF_BIAS handling fixes and sysfs i/f Rafael J. Wysocki
2019-03-21 22:18 ` [PATCH 1/2] PM / arch: x86: Rework the MSR_IA32_ENERGY_PERF_BIAS handling Rafael J. Wysocki
2019-03-22  9:03   ` Hannes Reinecke
2019-03-22 14:28   ` Borislav Petkov
2019-03-22 14:31     ` Thomas Gleixner
2019-03-22 14:35       ` Borislav Petkov
2019-03-22 16:12         ` Thomas Gleixner
2019-03-22 16:52           ` Joe Perches
2019-03-25 10:06     ` Rafael J. Wysocki
2019-03-22 16:27   ` Thomas Renninger
2019-03-22 16:43     ` Borislav Petkov
2019-03-25 11:31   ` Borislav Petkov
2019-03-21 22:20 ` [PATCH 2/2] PM / arch: x86: MSR_IA32_ENERGY_PERF_BIAS sysfs interface Rafael J. Wysocki
2019-03-22  9:03   ` Hannes Reinecke
2019-03-22 14:46   ` Borislav Petkov
2019-03-25 10:01     ` Rafael J. Wysocki
2019-03-22 15:00   ` Peter Zijlstra
2019-03-25  9:56     ` Rafael J. Wysocki
2019-03-25 11:32   ` Borislav Petkov
2019-05-09 10:23   ` Ido Schimmel
2019-05-09 17:18     ` Rafael J. Wysocki
2019-05-09 17:43       ` Ido Schimmel
2019-05-09 21:28         ` [PATCH] x86: intel_epb: Take CONFIG_PM into account Rafael J. Wysocki
2019-05-10  6:01           ` Ingo Molnar
2019-05-27 10:56         ` [PATCH] x86: intel_epb: Do not build when CONFIG_PM is unset Rafael J. Wysocki
2019-05-30  7:47           ` Ingo Molnar [this message]

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