linux-kernel - [PATCH v1 0/2] x86/smp: Fix power regression introduced by commit 96040f7273e2

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Message-ID: <2006806.PYKUYFuaPT@rjwysocki.net>
Date: Wed, 28 May 2025 14:53:13 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: x86 Maintainers <x86@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Linux PM <linux-pm@...r.kernel.org>,
 Len Brown <lenb@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...e.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
 "Gautham R. Shenoy" <gautham.shenoy@....com>, Ingo Molnar <mingo@...hat.com>,
 Todd Brandt <todd.e.brandt@...ux.intel.com>
Subject:
 [PATCH v1 0/2] x86/smp: Fix power regression introduced by commit
 96040f7273e2

Hi Everyone,

Commit 96040f7273e2 ("x86/smp: Eliminate mwait_play_dead_cpuid_hint()")
that shipped in 6.15 introduced a nasty power regression on systems that
start with "nosmt" in the kernel command line which prevents it from entering
deep package idle states (for instance, PC10) later on.  Idle power, including
power in suspend-to-idle, goes up significantly on those systems as a result.

Address this by reverting commit 96040f7273e2 (patch [1/2]) and using a
different approach, which is to retain mwait_play_dead_cpuid_hint() and
still prefer it to hlt_play_dead() in case it is needed when cpuidle is
not available, but prefer cpuidle_play_dead() to it by default (patch [2/2]).

Thanks!