linux-kernel - [PATCH v3 0/3] SRF: Fix offline CPU preventing pc6 entry

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Message-ID: <20241108122909.763663-1-patryk.wlazlyn@linux.intel.com>
Date: Fri,  8 Nov 2024 13:29:06 +0100
From: Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org,
	rafael.j.wysocki@...el.com,
	len.brown@...el.com,
	artem.bityutskiy@...ux.intel.com,
	dave.hansen@...ux.intel.com,
	patryk.wlazlyn@...ux.intel.com
Subject: [PATCH v3 0/3] SRF: Fix offline CPU preventing pc6 entry

Applied suggestions from Dave and Rafael.

Because we now call a smp function, we have to have ifdefs for
CONFIG_SMP or rely on mwait_play_dead_with_hint to return immediatelly
with an error on non-smp builds. I decided to do the later, but maybe we
should return -ENODEV (or other error constant) instead of 1. I am open
for suggestions.

Removing the existing "kexec hack" by bringing all offlined CPUs back
online before proceeding with the kexec would make it even simpler, but
I am not sure we can do that. It looks kind of obvious to me, but for
some reason the hack exist.

Changes since v2:
  The whole approach changed, but there main things are below.

  * Split mwait_play_dead (old code) into two parts:
    1. Computing mwait hint based on cpuid leaf 0x5
    2. Entering while(1) mwait loop with "kexec hack" handling

  * Prefer cpuidle_play_dead over mwait_play_dead by reordering calls in
    native_play_dead.

  * Add implementation for enter_dead() handler in intel_idle that calls
    executes old mwait_play_dead code, but with the mwait hint from the
    cpuidle state table.

Patryk Wlazlyn (3):
  x86/smp: Allow calling mwait_play_dead with arbitrary hint
  x86/smp native_play_dead: Prefer cpuidle_play_dead() over
    mwait_play_dead()
  intel_idle: Provide enter_dead() handler for SRF

 arch/x86/include/asm/smp.h |  6 ++++++
 arch/x86/kernel/smpboot.c  | 29 ++++++++++++++++++++---------
 drivers/idle/intel_idle.c  | 16 ++++++++++++++++
 3 files changed, 42 insertions(+), 9 deletions(-)

-- 
2.47.0