linux-kernel - [PATCH v2 1/3] x86/smp: Move mwait hint computation out of mwait_play

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Message-ID: <20241029101507.7188-2-patryk.wlazlyn@linux.intel.com>
Date: Tue, 29 Oct 2024 11:15:05 +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 v2 1/3] x86/smp: Move mwait hint computation out of mwait_play_dead

The following patches will provide a way for idle driver to set the
mwait hint for offline code to use to reach the deepest cstate.

Make the following changes simpler by moving the mwait hint computation
to a separate function.

Signed-off-by: Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>
---
 arch/x86/kernel/smpboot.c | 44 ++++++++++++++++++++++++---------------
 1 file changed, 27 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 0c35207320cb..683898e3b20e 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1270,28 +1270,14 @@ void play_dead_common(void)
 	local_irq_disable();
 }
 
-/*
- * We need to flush the caches before going to sleep, lest we have
- * dirty data in our caches when we come back up.
- */
-static inline void mwait_play_dead(void)
+/* Computes mwait hint for the deepest mwait hint based on cpuid leaf 0x5 */
+static inline unsigned int get_deepest_mwait_hint(void)
 {
-	struct mwait_cpu_dead *md = this_cpu_ptr(&mwait_cpu_dead);
 	unsigned int eax, ebx, ecx, edx;
 	unsigned int highest_cstate = 0;
 	unsigned int highest_subcstate = 0;
 	int i;
 
-	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
-	    boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
-		return;
-	if (!this_cpu_has(X86_FEATURE_MWAIT))
-		return;
-	if (!this_cpu_has(X86_FEATURE_CLFLUSH))
-		return;
-	if (__this_cpu_read(cpu_info.cpuid_level) < CPUID_MWAIT_LEAF)
-		return;
-
 	eax = CPUID_MWAIT_LEAF;
 	ecx = 0;
 	native_cpuid(&eax, &ebx, &ecx, &edx);
@@ -1314,6 +1300,30 @@ static inline void mwait_play_dead(void)
 			(highest_subcstate - 1);
 	}
 
+	return eax;
+}
+
+/*
+ * We need to flush the caches before going to sleep, lest we have
+ * dirty data in our caches when we come back up.
+ */
+static inline void mwait_play_dead(void)
+{
+	struct mwait_cpu_dead *md = this_cpu_ptr(&mwait_cpu_dead);
+	unsigned int hint;
+
+	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
+	    boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
+		return;
+	if (!this_cpu_has(X86_FEATURE_MWAIT))
+		return;
+	if (!this_cpu_has(X86_FEATURE_CLFLUSH))
+		return;
+	if (__this_cpu_read(cpu_info.cpuid_level) < CPUID_MWAIT_LEAF)
+		return;
+
+	hint = get_deepest_mwait_hint();
+
 	/* Set up state for the kexec() hack below */
 	md->status = CPUDEAD_MWAIT_WAIT;
 	md->control = CPUDEAD_MWAIT_WAIT;
@@ -1333,7 +1343,7 @@ static inline void mwait_play_dead(void)
 		mb();
 		__monitor(md, 0, 0);
 		mb();
-		__mwait(eax, 0);
+		__mwait(hint, 0);
 
 		if (READ_ONCE(md->control) == CPUDEAD_MWAIT_KEXEC_HLT) {
 			/*
-- 
2.47.0