lkml.org 
[lkml]   [2008]   [Feb]   [9]   [last100]   RSS-feed
Views: [more markup]  [less markup]  [headers]  [forward] 
 
Messages in this thread
Complete thread (EXPERIMENTAL)
/
DateSat, 9 Feb 2008 10:33:21 +0100 (CET)
FromThomas Gleixner <>
SubjectRe: [PATCH] x86: Simplify cpu_idle_wait
Digg This
On Fri, 8 Feb 2008, Venki Pallipadi wrote:

On Fri, Feb 08, 2008 at 11:28:48AM +0100, Andi Kleen wrote:

- 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, 0);

I think the last argument (wait) needs to be 1 to make sure it is synchronous (for 32/64) Otherwise the patch looks great.

Yes. Below is the updated patch

Applied. Thanks,

tglx

Earlier commit 40d6a146629b98d8e322b6f9332b182c7cbff3df 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>
Index: linux-2.6.25-rc/arch/x86/kernel/process_32.c =================================================================== --- linux-2.6.25-rc.orig/arch/x86/kernel/process_32.c +++ linux-2.6.25-rc/arch/x86/kernel/process_32.c
@@ -82,7 +82,6 @@ unsigned long thread_saved_pc(struct tas */
void (*pm_idle)(void);
EXPORT_SYMBOL(pm_idle);
-static DEFINE_PER_CPU(unsigned int, cpu_idle_state);
void disable_hlt(void)
{
@@ -181,9 +180,6 @@ 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;
@@ -208,40 +204,19 @@ 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);

Index: linux-2.6.25-rc/arch/x86/kernel/process_64.c =================================================================== --- linux-2.6.25-rc.orig/arch/x86/kernel/process_64.c +++ linux-2.6.25-rc/arch/x86/kernel/process_64.c
@@ -64,7 +64,6 @@ 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);

@@ -139,41 +138,19 @@ 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);

@@ -215,9 +192,6 @@ void cpu_idle (void)
while (!need_resched()) {
void (*idle)(void);

- if (__get_cpu_var(cpu_idle_state))
- __get_cpu_var(cpu_idle_state) = 0;
-
tick_nohz_stop_sched_tick();

rmb();




\
ISP Services
Valid XHTML 1.0!\ /
Valid CSS! Last update: 2008-02-09 10:37    [W:0.545 / U:0.260 seconds]
©2003-2005 Jasper Spaans