[patch 2/2] x86: put offline CPUs into deepest mwait cstate_subcstate

[venkatesh . pallipadi]

Offline CPUs can save power by going into deepest cstate, subcstate
instead of hlt loop.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx>
---
 arch/x86/kernel/acpi/cstate.c |   51 +++++++++++++++++++++++++++++++++++++++++
 1 files changed, 51 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
index bbbe4bb..5b0988a 100644
--- a/arch/x86/kernel/acpi/cstate.c
+++ b/arch/x86/kernel/acpi/cstate.c
@@ -150,6 +150,54 @@ void acpi_processor_ffh_cstate_enter(struct acpi_processor_cx *cx)
 }
 EXPORT_SYMBOL_GPL(acpi_processor_ffh_cstate_enter);
 
+static unsigned long mwait_play_dead_eax;
+
+static void mwait_play_dead(void)
+{
+	if (boot_cpu_data.x86 >= 4)
+		wbinvd();
+
+	while (1) {
+		__monitor((void *)&current_thread_info()->flags, 0, 0);
+		smp_mb();
+		__mwait(mwait_play_dead_eax, 0);
+	}
+}
+
+static void mwait_play_dead_init(void *unused)
+{
+	unsigned int eax, ebx, ecx, edx;
+	unsigned int highest_cstate = 0;
+	unsigned int highest_subcstate = 0;
+	int i;
+
+	if (!boot_cpu_has(X86_FEATURE_MWAIT))
+		return;
+	
+	if (boot_cpu_data.cpuid_level < CPUID_MWAIT_LEAF)
+		return;
+
+	pm_play_dead = mwait_play_dead;
+
+	cpuid(CPUID_MWAIT_LEAF, &eax, &ebx, &ecx, &edx);
+	/*
+	 * mwait_play_dead_eax will be 0 if EDX enumeration is not valid.
+	 * Initialized below to cstate, sub_cstate value when EDX is valid.
+	 */
+	if (!(ecx & 0x1))
+		return;
+		
+	edx >>= MWAIT_SUBSTATE_SIZE;
+	for (i = 0; i < 7 && edx; i++, edx >>= MWAIT_SUBSTATE_SIZE) {
+		if (edx & MWAIT_SUBSTATE_MASK) {
+			highest_cstate = i;
+			highest_subcstate = edx & MWAIT_SUBSTATE_MASK;
+		}
+	}
+	mwait_play_dead_eax = (highest_cstate << MWAIT_SUBSTATE_SIZE) |
+			      (highest_subcstate - 1);
+}
+
 static int __init ffh_cstate_init(void)
 {
 	struct cpuinfo_x86 *c = &boot_cpu_data;
@@ -157,6 +205,9 @@ static int __init ffh_cstate_init(void)
 		return -1;
 
 	cpu_cstate_entry = alloc_percpu(struct cstate_entry);
+
+	smp_call_function_single(0, mwait_play_dead_init, NULL, 1);
+
 	return 0;
 }
 
-- 
1.6.0.6

-- 

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