linux-kernel - [PATCH v3 2/3] x86/smp native_play_dead: Prefer cpuidle_play_dead() over mwait_play

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Message-ID: <20241108122909.763663-3-patryk.wlazlyn@linux.intel.com>
Date: Fri,  8 Nov 2024 13:29:08 +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 2/3] x86/smp native_play_dead: Prefer cpuidle_play_dead() over mwait_play_dead()

The generic implementation, based on cpuid leaf 0x5, for looking up the
mwait hint for the deepest cstate, depends on them to be continuous in
range [0, NUM_SUBSTATES-1]. While that is correct on most Intel x86
platforms, it is not architectural and may not result in reaching the
most optimized idle state on some of them.

Prefer cpuidle_play_dead() over the generic mwait_play_dead() loop and
fallback to the later in case of missing enter_dead() handler.

Signed-off-by: Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>
---
 arch/x86/kernel/smpboot.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 44c40781bad6..721bb931181c 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1416,9 +1416,9 @@ void native_play_dead(void)
 	play_dead_common();
 	tboot_shutdown(TB_SHUTDOWN_WFS);
 
-	mwait_play_dead();
 	if (cpuidle_play_dead())
-		hlt_play_dead();
+		mwait_play_dead();
+	hlt_play_dead();
 }
 
 #else /* ... !CONFIG_HOTPLUG_CPU */
-- 
2.47.0