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x86: Simplify cpu_idle_wait

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This patch also resolves hangs on boot:
	http://lkml.org/lkml/2008/2/23/263
	http://bugzilla.kernel.org/show_bug.cgi?id=10093

The bug was causing once-in-few-reboots 10-15 sec wait during boot on
certain laptops.

Earlier commit 40d6a14662 added
smp_call_function in cpu_idle_wait() to kick cpus that are in tickless
idle.  Looking at cpu_idle_wait code at that time, code seemed to be
over-engineered for a case which is rarely used (while changing idle
handler).

Below is a simplified version of cpu_idle_wait, which just makes a dummy
smp_call_function to all cpus, to make them come out of old idle handler
and start using the new idle handler.  It eliminates code in the idle
loop to handle cpu_idle_wait.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Venki Pallipadi 2008-04-10 09:49:58 -07:00 committed by Linus Torvalds
parent a1e58bbdc9
commit 783e391b7b
2 changed files with 22 additions and 72 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

47
arch/x86/kernel/process_32.c
View file

@ -82,7 +82,6 @@ unsigned long thread_saved_pc(struct task_struct *tsk)
*/
void (*pm_idle)(void);
EXPORT_SYMBOL(pm_idle);
static DEFINE_PER_CPU(unsigned int, cpu_idle_state);
void disable_hlt(void)
{
@ -190,9 +189,6 @@ void cpu_idle(void)
while (!need_resched()) {
void (*idle)(void);
if (__get_cpu_var(cpu_idle_state))
__get_cpu_var(cpu_idle_state) = 0;
check_pgt_cache();
rmb();
idle = pm_idle;
@ -220,40 +216,19 @@ static void do_nothing(void *unused)
{
}
/*
* cpu_idle_wait - Used to ensure that all the CPUs discard old value of
* pm_idle and update to new pm_idle value. Required while changing pm_idle
* handler on SMP systems.
*
* Caller must have changed pm_idle to the new value before the call. Old
* pm_idle value will not be used by any CPU after the return of this function.
*/
void cpu_idle_wait(void)
{
unsigned int cpu, this_cpu = get_cpu();
cpumask_t map, tmp = current->cpus_allowed;
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);
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);
/*
* We waited 1 sec, if a CPU still did not call idle
* it may be because it is in idle and not waking up
* because it has nothing to do.
* Give all the remaining CPUS a kick.
*/
smp_call_function_mask(map, do_nothing, NULL, 0);
} while (!cpus_empty(map));
set_cpus_allowed(current, tmp);
smp_mb();
/* kick all the CPUs so that they exit out of pm_idle */
smp_call_function(do_nothing, NULL, 0, 1);
}
EXPORT_SYMBOL_GPL(cpu_idle_wait);

47
arch/x86/kernel/process_64.c
View file

@ -63,7 +63,6 @@ EXPORT_SYMBOL(boot_option_idle_override);
*/
void (*pm_idle)(void);
EXPORT_SYMBOL(pm_idle);
static DEFINE_PER_CPU(unsigned int, cpu_idle_state);
static ATOMIC_NOTIFIER_HEAD(idle_notifier);
@ -173,9 +172,6 @@ void cpu_idle(void)
while (!need_resched()) {
void (*idle)(void);
if (__get_cpu_var(cpu_idle_state))
__get_cpu_var(cpu_idle_state) = 0;
rmb();
idle = pm_idle;
if (!idle)
@ -207,40 +203,19 @@ static void do_nothing(void *unused)
{
}
/*
* cpu_idle_wait - Used to ensure that all the CPUs discard old value of
* pm_idle and update to new pm_idle value. Required while changing pm_idle
* handler on SMP systems.
*
* Caller must have changed pm_idle to the new value before the call. Old
* pm_idle value will not be used by any CPU after the return of this function.
*/
void cpu_idle_wait(void)
{
unsigned int cpu, this_cpu = get_cpu();
cpumask_t map, tmp = current->cpus_allowed;
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);
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);
/*
* We waited 1 sec, if a CPU still did not call idle
* it may be because it is in idle and not waking up
* because it has nothing to do.
* Give all the remaining CPUS a kick.
*/
smp_call_function_mask(map, do_nothing, 0, 0);
} while (!cpus_empty(map));
set_cpus_allowed(current, tmp);
smp_mb();
/* kick all the CPUs so that they exit out of pm_idle */
smp_call_function(do_nothing, NULL, 0, 1);
}
EXPORT_SYMBOL_GPL(cpu_idle_wait);