* [PATCH] sched: Initialize rq->age_stamp on processor start
@ 2014-03-18 0:05 minyard
2014-03-18 4:06 ` Mike Galbraith
0 siblings, 1 reply; 9+ messages in thread
From: minyard @ 2014-03-18 0:05 UTC (permalink / raw)
To: linux-kernel; +Cc: Corey Minyard
From: Corey Minyard <cminyard@mvista.com>
If the sched_clock time starts at a large value, the kernel will spin
in sched_avg_update for a long time while rq->age_stamp catches up
with rq->clock.
The comment in kernel/sched/clock.c says that there is no strict promise
that it starts at zero. So initialize rq->age_stamp when a cpu starts up
to avoid this.
I was seeing long delays on a simulator that didn't start the clock at
zero. This might also be an issue on reboots on processors that don't
re-initialize the timer to zero on reset, and when using kexec.
Signed-off-by: Corey Minyard <cminyard@mvista.com>
---
kernel/sched/core.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b46131e..5be3d4a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5037,11 +5037,20 @@ static struct notifier_block migration_notifier = {
.priority = CPU_PRI_MIGRATION,
};
+static void __cpuinit set_cpu_rq_start_time(void)
+{
+ int cpu = smp_processor_id();
+ struct rq *rq = cpu_rq(cpu);
+ rq->age_stamp = sched_clock_cpu(cpu);
+}
+
static int sched_cpu_active(struct notifier_block *nfb,
unsigned long action, void *hcpu)
{
switch (action & ~CPU_TASKS_FROZEN) {
case CPU_STARTING:
+ set_cpu_rq_start_time();
+ /* fall through */
case CPU_DOWN_FAILED:
set_cpu_active((long)hcpu, true);
return NOTIFY_OK;
@@ -6922,6 +6931,7 @@ void __init sched_init(void)
init_sched_fair_class();
scheduler_running = 1;
+ set_cpu_rq_start_time();
}
#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
--
1.8.3.1
^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [PATCH] sched: Initialize rq->age_stamp on processor start
2014-03-18 0:05 [PATCH] sched: Initialize rq->age_stamp on processor start minyard
@ 2014-03-18 4:06 ` Mike Galbraith
2014-03-18 8:56 ` Peter Zijlstra
0 siblings, 1 reply; 9+ messages in thread
From: Mike Galbraith @ 2014-03-18 4:06 UTC (permalink / raw)
To: minyard; +Cc: linux-kernel, Corey Minyard, Peter Zijlstra
CC maintainer improves patch aerodynamics.
On Mon, 2014-03-17 at 19:05 -0500, minyard@acm.org wrote:
> From: Corey Minyard <cminyard@mvista.com>
>
> If the sched_clock time starts at a large value, the kernel will spin
> in sched_avg_update for a long time while rq->age_stamp catches up
> with rq->clock.
>
> The comment in kernel/sched/clock.c says that there is no strict promise
> that it starts at zero. So initialize rq->age_stamp when a cpu starts up
> to avoid this.
>
> I was seeing long delays on a simulator that didn't start the clock at
> zero. This might also be an issue on reboots on processors that don't
> re-initialize the timer to zero on reset, and when using kexec.
>
> Signed-off-by: Corey Minyard <cminyard@mvista.com>
> ---
> kernel/sched/core.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index b46131e..5be3d4a 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -5037,11 +5037,20 @@ static struct notifier_block migration_notifier = {
> .priority = CPU_PRI_MIGRATION,
> };
>
> +static void __cpuinit set_cpu_rq_start_time(void)
> +{
> + int cpu = smp_processor_id();
> + struct rq *rq = cpu_rq(cpu);
> + rq->age_stamp = sched_clock_cpu(cpu);
> +}
rq->age_stamp must lag rq->clock. See scale_rt_power(), and what
happens when it munches magic timewarp mushrooms.
> +
> static int sched_cpu_active(struct notifier_block *nfb,
> unsigned long action, void *hcpu)
> {
> switch (action & ~CPU_TASKS_FROZEN) {
> case CPU_STARTING:
> + set_cpu_rq_start_time();
> + /* fall through */
> case CPU_DOWN_FAILED:
> set_cpu_active((long)hcpu, true);
> return NOTIFY_OK;
> @@ -6922,6 +6931,7 @@ void __init sched_init(void)
> init_sched_fair_class();
>
> scheduler_running = 1;
> + set_cpu_rq_start_time();
> }
>
> #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] sched: Initialize rq->age_stamp on processor start
2014-03-18 4:06 ` Mike Galbraith
@ 2014-03-18 8:56 ` Peter Zijlstra
2014-03-18 9:25 ` Mike Galbraith
0 siblings, 1 reply; 9+ messages in thread
From: Peter Zijlstra @ 2014-03-18 8:56 UTC (permalink / raw)
To: Mike Galbraith; +Cc: minyard, linux-kernel, Corey Minyard
On Tue, Mar 18, 2014 at 05:06:26AM +0100, Mike Galbraith wrote:
> CC maintainer improves patch aerodynamics.
hehe, for sure. I have very little time to look at lkml these days and
there's a near 100% chance I'll miss anything that doesn't hit the
inbox.
> On Mon, 2014-03-17 at 19:05 -0500, minyard@acm.org wrote:
> > From: Corey Minyard <cminyard@mvista.com>
> >
> > If the sched_clock time starts at a large value, the kernel will spin
> > in sched_avg_update for a long time while rq->age_stamp catches up
> > with rq->clock.
> >
> > The comment in kernel/sched/clock.c says that there is no strict promise
> > that it starts at zero. So initialize rq->age_stamp when a cpu starts up
> > to avoid this.
> >
> > I was seeing long delays on a simulator that didn't start the clock at
> > zero. This might also be an issue on reboots on processors that don't
> > re-initialize the timer to zero on reset, and when using kexec.
> >
> > Signed-off-by: Corey Minyard <cminyard@mvista.com>
> > ---
> > kernel/sched/core.c | 10 ++++++++++
> > 1 file changed, 10 insertions(+)
> >
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index b46131e..5be3d4a 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -5037,11 +5037,20 @@ static struct notifier_block migration_notifier = {
> > .priority = CPU_PRI_MIGRATION,
> > };
> >
> > +static void __cpuinit set_cpu_rq_start_time(void)
> > +{
> > + int cpu = smp_processor_id();
> > + struct rq *rq = cpu_rq(cpu);
> > + rq->age_stamp = sched_clock_cpu(cpu);
> > +}
>
> rq->age_stamp must lag rq->clock. See scale_rt_power(), and what
> happens when it munches magic timewarp mushrooms.
>
> > +
> > static int sched_cpu_active(struct notifier_block *nfb,
> > unsigned long action, void *hcpu)
> > {
> > switch (action & ~CPU_TASKS_FROZEN) {
> > case CPU_STARTING:
> > + set_cpu_rq_start_time();
> > + /* fall through */
> > case CPU_DOWN_FAILED:
> > set_cpu_active((long)hcpu, true);
> > return NOTIFY_OK;
> > @@ -6922,6 +6931,7 @@ void __init sched_init(void)
> > init_sched_fair_class();
> >
> > scheduler_running = 1;
> > + set_cpu_rq_start_time();
I would put it one line up; that scheduler_running=1 is the last thing
we should do.
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] sched: Initialize rq->age_stamp on processor start
2014-03-18 8:56 ` Peter Zijlstra
@ 2014-03-18 9:25 ` Mike Galbraith
0 siblings, 0 replies; 9+ messages in thread
From: Mike Galbraith @ 2014-03-18 9:25 UTC (permalink / raw)
To: Peter Zijlstra; +Cc: minyard, linux-kernel, Corey Minyard
On Tue, 2014-03-18 at 09:56 +0100, Peter Zijlstra wrote:
> On Tue, Mar 18, 2014 at 05:06:26AM +0100, Mike Galbraith wrote:
> > > +static void __cpuinit set_cpu_rq_start_time(void)
> > > +{
> > > + int cpu = smp_processor_id();
> > > + struct rq *rq = cpu_rq(cpu);
> > > + rq->age_stamp = sched_clock_cpu(cpu);
> > > +}
> >
> > rq->age_stamp must lag rq->clock. See scale_rt_power(), and what
> > happens when it munches magic timewarp mushrooms.
> >
> > > +
> > > static int sched_cpu_active(struct notifier_block *nfb,
> > > unsigned long action, void *hcpu)
> > > {
> > > switch (action & ~CPU_TASKS_FROZEN) {
> > > case CPU_STARTING:
> > > + set_cpu_rq_start_time();
> > > + /* fall through */
> > > case CPU_DOWN_FAILED:
> > > set_cpu_active((long)hcpu, true);
> > > return NOTIFY_OK;
> > > @@ -6922,6 +6931,7 @@ void __init sched_init(void)
> > > init_sched_fair_class();
> > >
> > > scheduler_running = 1;
> > > + set_cpu_rq_start_time();
>
> I would put it one line up; that scheduler_running=1 is the last thing
> we should do.
And set clock and age, dazed scale_rt_power() is butt ugly.
-Mike
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] sched: Initialize rq->age_stamp on processor start
2014-05-08 18:47 ` minyard
@ 2014-05-09 9:12 ` Peter Zijlstra
0 siblings, 0 replies; 9+ messages in thread
From: Peter Zijlstra @ 2014-05-09 9:12 UTC (permalink / raw)
To: minyard; +Cc: Ingo Molnar, linux-kernel, Corey Minyard
[-- Attachment #1: Type: text/plain, Size: 739 bytes --]
On Thu, May 08, 2014 at 01:47:39PM -0500, minyard@acm.org wrote:
> From: Corey Minyard <cminyard@mvista.com>
>
> If the sched_clock time starts at a large value, the kernel will spin
> in sched_avg_update for a long time while rq->age_stamp catches up
> with rq->clock.
>
> The comment in kernel/sched/clock.c says that there is no strict promise
> that it starts at zero. So initialize rq->age_stamp when a cpu starts up
> to avoid this.
>
> I was seeing long delays on a simulator that didn't start the clock at
> zero. This might also be an issue on reboots on processors that don't
> re-initialize the timer to zero on reset, and when using kexec.
>
> Signed-off-by: Corey Minyard <cminyard@mvista.com>
Thanks
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^ permalink raw reply [flat|nested] 9+ messages in thread
* [PATCH] sched: Initialize rq->age_stamp on processor start
2014-05-08 16:13 ` Peter Zijlstra
2014-05-08 18:47 ` Corey Minyard
@ 2014-05-08 18:47 ` minyard
2014-05-09 9:12 ` Peter Zijlstra
1 sibling, 1 reply; 9+ messages in thread
From: minyard @ 2014-05-08 18:47 UTC (permalink / raw)
To: Ingo Molnar, Peter Zijlstra; +Cc: linux-kernel, Corey Minyard
From: Corey Minyard <cminyard@mvista.com>
If the sched_clock time starts at a large value, the kernel will spin
in sched_avg_update for a long time while rq->age_stamp catches up
with rq->clock.
The comment in kernel/sched/clock.c says that there is no strict promise
that it starts at zero. So initialize rq->age_stamp when a cpu starts up
to avoid this.
I was seeing long delays on a simulator that didn't start the clock at
zero. This might also be an issue on reboots on processors that don't
re-initialize the timer to zero on reset, and when using kexec.
Signed-off-by: Corey Minyard <cminyard@mvista.com>
---
kernel/sched/core.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 268a45e..80725c9 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5039,11 +5039,20 @@ static struct notifier_block migration_notifier = {
.priority = CPU_PRI_MIGRATION,
};
+static void __cpuinit set_cpu_rq_start_time(void)
+{
+ int cpu = smp_processor_id();
+ struct rq *rq = cpu_rq(cpu);
+ rq->age_stamp = sched_clock_cpu(cpu);
+}
+
static int sched_cpu_active(struct notifier_block *nfb,
unsigned long action, void *hcpu)
{
switch (action & ~CPU_TASKS_FROZEN) {
case CPU_STARTING:
+ set_cpu_rq_start_time();
+ /* fall through */
case CPU_DOWN_FAILED:
set_cpu_active((long)hcpu, true);
return NOTIFY_OK;
@@ -6919,6 +6928,7 @@ void __init sched_init(void)
if (cpu_isolated_map == NULL)
zalloc_cpumask_var(&cpu_isolated_map, GFP_NOWAIT);
idle_thread_set_boot_cpu();
+ set_cpu_rq_start_time();
#endif
init_sched_fair_class();
--
1.8.3.1
^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [PATCH] sched: Initialize rq->age_stamp on processor start
2014-05-08 16:13 ` Peter Zijlstra
@ 2014-05-08 18:47 ` Corey Minyard
2014-05-08 18:47 ` minyard
1 sibling, 0 replies; 9+ messages in thread
From: Corey Minyard @ 2014-05-08 18:47 UTC (permalink / raw)
To: Peter Zijlstra, minyard; +Cc: Ingo Molnar, linux-kernel
On 05/08/2014 11:13 AM, Peter Zijlstra wrote:
> On Tue, May 06, 2014 at 02:50:57PM -0500, minyard@acm.org wrote:
>> From: Corey Minyard <cminyard@mvista.com>
>>
>> If the sched_clock time starts at a large value, the kernel will spin
>> in sched_avg_update for a long time while rq->age_stamp catches up
>> with rq->clock.
>>
>> The comment in kernel/sched/clock.c says that there is no strict promise
>> that it starts at zero. So initialize rq->age_stamp when a cpu starts up
>> to avoid this.
>>
>> I was seeing long delays on a simulator that didn't start the clock at
>> zero. This might also be an issue on reboots on processors that don't
>> re-initialize the timer to zero on reset, and when using kexec.
>>
>> Signed-off-by: Corey Minyard <cminyard@mvista.com>
> This patch made my cris-defconfig build fail.
Dang, I missed propagating a change. Yes, it's broken. One more time...
-corey
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] sched: Initialize rq->age_stamp on processor start
2014-05-06 19:50 minyard
@ 2014-05-08 16:13 ` Peter Zijlstra
2014-05-08 18:47 ` Corey Minyard
2014-05-08 18:47 ` minyard
0 siblings, 2 replies; 9+ messages in thread
From: Peter Zijlstra @ 2014-05-08 16:13 UTC (permalink / raw)
To: minyard; +Cc: Ingo Molnar, linux-kernel, Corey Minyard
[-- Attachment #1: Type: text/plain, Size: 778 bytes --]
On Tue, May 06, 2014 at 02:50:57PM -0500, minyard@acm.org wrote:
> From: Corey Minyard <cminyard@mvista.com>
>
> If the sched_clock time starts at a large value, the kernel will spin
> in sched_avg_update for a long time while rq->age_stamp catches up
> with rq->clock.
>
> The comment in kernel/sched/clock.c says that there is no strict promise
> that it starts at zero. So initialize rq->age_stamp when a cpu starts up
> to avoid this.
>
> I was seeing long delays on a simulator that didn't start the clock at
> zero. This might also be an issue on reboots on processors that don't
> re-initialize the timer to zero on reset, and when using kexec.
>
> Signed-off-by: Corey Minyard <cminyard@mvista.com>
This patch made my cris-defconfig build fail.
[-- Attachment #2: Type: application/pgp-signature, Size: 836 bytes --]
^ permalink raw reply [flat|nested] 9+ messages in thread
* [PATCH] sched: Initialize rq->age_stamp on processor start
@ 2014-05-06 19:50 minyard
2014-05-08 16:13 ` Peter Zijlstra
0 siblings, 1 reply; 9+ messages in thread
From: minyard @ 2014-05-06 19:50 UTC (permalink / raw)
To: Ingo Molnar, Peter Zijlstra; +Cc: linux-kernel, Corey Minyard
From: Corey Minyard <cminyard@mvista.com>
If the sched_clock time starts at a large value, the kernel will spin
in sched_avg_update for a long time while rq->age_stamp catches up
with rq->clock.
The comment in kernel/sched/clock.c says that there is no strict promise
that it starts at zero. So initialize rq->age_stamp when a cpu starts up
to avoid this.
I was seeing long delays on a simulator that didn't start the clock at
zero. This might also be an issue on reboots on processors that don't
re-initialize the timer to zero on reset, and when using kexec.
Signed-off-by: Corey Minyard <cminyard@mvista.com>
---
kernel/sched/core.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 268a45e..6e9570b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5039,11 +5039,20 @@ static struct notifier_block migration_notifier = {
.priority = CPU_PRI_MIGRATION,
};
+static void __cpuinit set_cpu_rq_start_time(void)
+{
+ int cpu = smp_processor_id();
+ struct rq *rq = cpu_rq(cpu);
+ rq->age_stamp = sched_clock_cpu(cpu);
+}
+
static int sched_cpu_active(struct notifier_block *nfb,
unsigned long action, void *hcpu)
{
switch (action & ~CPU_TASKS_FROZEN) {
case CPU_STARTING:
+ set_cpu_rq_start_time();
+ /* fall through */
case CPU_DOWN_FAILED:
set_cpu_active((long)hcpu, true);
return NOTIFY_OK;
@@ -6923,6 +6932,7 @@ void __init sched_init(void)
init_sched_fair_class();
scheduler_running = 1;
+ set_cpu_rq_start_time();
}
#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
--
1.8.3.1
^ permalink raw reply related [flat|nested] 9+ messages in thread
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2014-03-18 0:05 [PATCH] sched: Initialize rq->age_stamp on processor start minyard
2014-03-18 4:06 ` Mike Galbraith
2014-03-18 8:56 ` Peter Zijlstra
2014-03-18 9:25 ` Mike Galbraith
2014-05-06 19:50 minyard
2014-05-08 16:13 ` Peter Zijlstra
2014-05-08 18:47 ` Corey Minyard
2014-05-08 18:47 ` minyard
2014-05-09 9:12 ` Peter Zijlstra
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