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Date:	Tue, 10 Nov 2009 14:12:41 +0800
From:	Luming Yu <>
To:	LKML <>
Cc:	Len Brown <>,
	"Pallipadi, Venkatesh" <>,
	"Siddha, Suresh B" <>,
	Arjan van de Ven <>
Subject: [RFC PATCH] use acpi_idle_enter_simple if bm_check && !.bm_control

Hi there,

I came across acpi processor idle driver, noticed that we can cut a
bit overhead at C3 entry that can improve C3 residency a bit,
especially when it has similar kernel config as old RHEL 5 kernel
(2.6.18) on systems with as many as 64 logical CPUs. The point of this
patch is bm_sts is an optional bit. It never returns 1 on systems with
bm_check && !bm_control I tested. Instead, I have observed lower C3
residency due to accessing bm_sts and relevant code on a system with
64 logical CPUs with HZ=1000. Please review. If make sense, please

Ps. The patch is enclosed in attachment. The in-lined one is c&p of it
for reading.


Signed-off-by: Yu Luming <>

 processor_idle.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

 processor_idle.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
[root@...core tmp]# cat 12.patch
diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index 66393d5..ee72bbb 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -895,7 +895,7 @@ static int acpi_idle_enter_simple(struct
cpuidle_device *dev,
 	lapic_timer_state_broadcast(pr, cx, 1);

-	if (cx->type == ACPI_STATE_C3)
+	if (cx->type == ACPI_STATE_C3 && !pr->flags.bm_check)

 	kt1 = ktime_get_real();
@@ -1110,6 +1110,8 @@ static int acpi_processor_setup_cpuidle(struct
acpi_processor *pr)
 			state->enter = pr->flags.bm_check ?
 					acpi_idle_enter_bm :
+			if (pr->flags.bm_check && !pr->flags.bm_control)
+				state->enter = acpi_idle_enter_simple;

Download attachment "12.patch" of type "application/octet-stream" (754 bytes)

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