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Message-ID: <20080208172430.GA8302@linux-os.sc.intel.com>
Date: Fri, 8 Feb 2008 09:24:30 -0800
From: Venki Pallipadi <venkatesh.pallipadi@...el.com>
To: Andi Kleen <ak@...e.de>
Cc: Venki Pallipadi <venkatesh.pallipadi@...el.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Steven Rostedt <rostedt@...dmis.org>,
LKML <linux-kernel@...r.kernel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Ingo Molnar <mingo@...e.hu>,
Thomas Gleixner <tglx@...utronix.de>,
"Brown, Len" <len.brown@...el.com>, Adam Belay <abelay@...ell.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] x86: Simplify cpu_idle_wait
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
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@...el.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();
--
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