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Message-ID: <20080410164958.GA24586@linux-os.sc.intel.com>
Date: Thu, 10 Apr 2008 09:49:58 -0700
From: Venki Pallipadi <venkatesh.pallipadi@...el.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: "Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
Andi Kleen <ak@...e.de>,
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>,
"Brown, Len" <len.brown@...el.com>, Adam Belay <abelay@...ell.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Len Brown <lenb@...nel.org>, rjw@...k.pl
Subject: Re: [PATCH] x86: Simplify cpu_idle_wait
On Sat, Feb 09, 2008 at 02:33:21AM -0700, Thomas Gleixner wrote:
> 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
thomas/ingo/hpa,
Looks like this patch never made it to mainline.
The earlier patch does not apply cleanly to mainline any more. Below is the
updated patch.
Thanks,
Venki
As a bonus, this patch seems to resolve the bug reported here
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 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>
---
arch/x86/kernel/process_32.c | 47 ++++++++++---------------------------------
arch/x86/kernel/process_64.c | 47 ++++++++++---------------------------------
2 files changed, 22 insertions(+), 72 deletions(-)
Index: linux-2.6/arch/x86/kernel/process_32.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/process_32.c 2008-03-24 04:40:54.000000000 -0700
+++ linux-2.6/arch/x86/kernel/process_32.c 2008-04-09 10:06:03.000000000 -0700
@@ -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)
{
@@ -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);
Index: linux-2.6/arch/x86/kernel/process_64.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/process_64.c 2008-03-24 04:40:54.000000000 -0700
+++ linux-2.6/arch/x86/kernel/process_64.c 2008-04-09 10:07:48.000000000 -0700
@@ -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);
--
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