From: Zwane Mwaikambo 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 Signed-off-by: Andrew Morton --- arch/ia64/kernel/process.c | 41 ++++++++++++++++++++++++++--------------- 1 files changed, 26 insertions(+), 15 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 2005-04-26 01:24:15.974759736 -0700 +++ 25-akpm/arch/ia64/kernel/process.c 2005-04-26 01:24:15.978759128 -0700 @@ -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_state); unsigned long boot_option_idle_override = 0; EXPORT_SYMBOL(boot_option_idle_override); @@ -224,20 +224,31 @@ 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); @@ -245,7 +256,6 @@ void __attribute__((noreturn)) cpu_idle (void) { void (*mark_idle)(int) = ia64_mark_idle; - int cpu = smp_processor_id(); /* endless idle loop with no priority at all */ while (1) { @@ -256,12 +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; _