From: Zwane Mwaikambo <zwane@arm.linux.org.uk>
Andi noted that during normal runtime cpu_idle_map is bounced around a lot,
and occassionally at a higher frequency than the timer interrupt wakeup
which we normally exit pm_idle from. So switch to a percpu variable.
I didn't move things to the slow path because it would involve adding
scheduler code to wakeup the idle thread on the cpus we're waiting for.
Signed-off-by: Zwane Mwaikambo <zwane@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/arch/ia64/kernel/process.c | 40 ++++++++++++++++++++++++-------------
1 files changed, 26 insertions(+), 14 deletions(-)
diff -puN arch/ia64/kernel/process.c~ia64-reduce-cacheline-bouncing-in-cpu_idle_wait arch/ia64/kernel/process.c
--- 25/arch/ia64/kernel/process.c~ia64-reduce-cacheline-bouncing-in-cpu_idle_wait 2005-03-10 22:46:04.000000000 -0800
+++ 25-akpm/arch/ia64/kernel/process.c 2005-03-10 22:46:04.000000000 -0800
@@ -50,7 +50,7 @@
#include "sigframe.h"
void (*ia64_mark_idle)(int);
-static cpumask_t cpu_idle_map;
+static DEFINE_PER_CPU(unsigned int, cpu_idle_map);
unsigned long boot_option_idle_override = 0;
EXPORT_SYMBOL(boot_option_idle_override);
@@ -223,20 +223,31 @@ static inline void play_dead(void)
}
#endif /* CONFIG_HOTPLUG_CPU */
-
void cpu_idle_wait(void)
{
- int cpu;
- cpumask_t map;
+ unsigned int cpu, this_cpu = get_cpu();
+ cpumask_t map;
+
+ set_cpus_allowed(current, cpumask_of_cpu(this_cpu));
+ put_cpu();
- for_each_online_cpu(cpu)
- cpu_set(cpu, cpu_idle_map);
+ cpus_clear(map);
+ for_each_online_cpu(cpu) {
+ per_cpu(cpu_idle_state, cpu) = 1;
+ cpu_set(cpu, map);
+ }
- wmb();
- do {
- ssleep(1);
- cpus_and(map, cpu_idle_map, cpu_online_map);
- } while (!cpus_empty(map));
+ __get_cpu_var(cpu_idle_state) = 0;
+
+ wmb();
+ do {
+ ssleep(1);
+ for_each_online_cpu(cpu) {
+ if (cpu_isset(cpu, map) && !per_cpu(cpu_idle_state, cpu))
+ cpu_clear(cpu, map);
+ }
+ cpus_and(map, map, cpu_online_map);
+ } while (!cpus_empty(map));
}
EXPORT_SYMBOL_GPL(cpu_idle_wait);
@@ -255,12 +266,13 @@ cpu_idle (void)
while (!need_resched()) {
void (*idle)(void);
+ if (__get_cpu_var(cpu_idle_state))
+ __get_cpu_var(cpu_idle_state) = 0;
+
+ rmb();
if (mark_idle)
(*mark_idle)(1);
- if (cpu_isset(cpu, cpu_idle_map))
- cpu_clear(cpu, cpu_idle_map);
- rmb();
idle = pm_idle;
if (!idle)
idle = default_idle;
_