[Xen-devel] [PATCH]cpuidle: Fix possible false judge caused by type casting

["Wei, Gang" <gang.wei@xxxxxxxxx>]

Keir, this is a fix along with an added tuning option. It should not have any 
negative impact. Could you take it in 3.4?

Jimmy

cpuidle: Fix possible false judge caused by type casting

For timer_deadline == 0 or timer_deadline - now > largest u32 case,
the expected_us (in u32 type) may become wrong.

Add a tunable option to ease conditional adjustment.

Signed-off-by: Wei Gang <gang.wei@xxxxxxxxx>

diff -r fb3e1e84d8f4 xen/arch/x86/acpi/cpu_idle.c
--- a/xen/arch/x86/acpi/cpu_idle.c      Wed May 06 12:40:51 2009 +0100
+++ b/xen/arch/x86/acpi/cpu_idle.c      Thu May 14 17:36:11 2009 +0800
@@ -624,6 +624,7 @@ static int check_cx(struct acpi_processo
 }
 
 static unsigned int latency_factor = 2;
+integer_param("idle_latency_factor", latency_factor);
 
 static void set_cx(
     struct acpi_processor_power *acpi_power,
diff -r fb3e1e84d8f4 xen/arch/x86/acpi/cpuidle_menu.c
--- a/xen/arch/x86/acpi/cpuidle_menu.c  Wed May 06 12:40:51 2009 +0100
+++ b/xen/arch/x86/acpi/cpuidle_menu.c  Thu May 14 17:36:11 2009 +0800
@@ -45,9 +45,15 @@ struct menu_device
 
 static DEFINE_PER_CPU(struct menu_device, menu_devices);
 
-static s_time_t get_sleep_length_ns(void)
+static unsigned int get_sleep_length_us(void)
 {
-    return per_cpu(timer_deadline, smp_processor_id()) - NOW();
+    s_time_t us = (per_cpu(timer_deadline, smp_processor_id()) - NOW()) / 1000;
+    /*
+     * while us < 0 or us > (u32)-1, return a large u32,
+     * choose (unsigned int)-2000 to avoid wrapping while added with exit
+     * latency because the latency should not larger than 2ms
+     */
+    return (us >> 32) ? (unsigned int)-2000 : (unsigned int)us;
 }
 
 static int menu_select(struct acpi_processor_power *power)
@@ -56,7 +62,7 @@ static int menu_select(struct acpi_proce
     int i;
 
     /* determine the expected residency time */
-    data->expected_us = (u32) get_sleep_length_ns() / 1000;
+    data->expected_us = get_sleep_length_us();
 
     /* find the deepest idle state that satisfies our constraints */
     for ( i = 2; i < power->count; i++ )

Attachment: fix-for-menu.patch
Description: fix-for-menu.patch

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