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/i386/kernel/process.c | 29 +++++++++++++++++++++--------
1 files changed, 21 insertions(+), 8 deletions(-)
diff -puN arch/i386/kernel/process.c~x86-reduce-cacheline-bouncing-in-cpu_idle_wait arch/i386/kernel/process.c
--- 25/arch/i386/kernel/process.c~x86-reduce-cacheline-bouncing-in-cpu_idle_wait 2005-03-10 22:45:35.000000000 -0800
+++ 25-akpm/arch/i386/kernel/process.c 2005-03-10 22:45:35.000000000 -0800
@@ -78,7 +78,7 @@ unsigned long thread_saved_pc(struct tas
* Powermanagement idle function, if any..
*/
void (*pm_idle)(void);
-static cpumask_t cpu_idle_map;
+static DEFINE_PER_CPU(unsigned int, cpu_idle_state);
void disable_hlt(void)
{
@@ -185,9 +185,10 @@ void cpu_idle (void)
while (1) {
while (!need_resched()) {
void (*idle)(void);
-
- if (cpu_isset(cpu, cpu_idle_map))
- cpu_clear(cpu, cpu_idle_map);
+
+ if (__get_cpu_var(cpu_idle_state))
+ __get_cpu_var(cpu_idle_state) = 0;
+
rmb();
idle = pm_idle;
@@ -206,16 +207,28 @@ void cpu_idle (void)
void cpu_idle_wait(void)
{
- int cpu;
+ unsigned int cpu, this_cpu = get_cpu();
cpumask_t map;
- for_each_online_cpu(cpu)
- cpu_set(cpu, cpu_idle_map);
+ set_cpus_allowed(current, cpumask_of_cpu(this_cpu));
+ put_cpu();
+
+ cpus_clear(map);
+ for_each_online_cpu(cpu) {
+ per_cpu(cpu_idle_state, cpu) = 1;
+ cpu_set(cpu, map);
+ }
+
+ __get_cpu_var(cpu_idle_state) = 0;
wmb();
do {
ssleep(1);
- cpus_and(map, cpu_idle_map, cpu_online_map);
+ 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);
_