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[PATCH 0/2] nohz_full: Offload task_tick to remote housekeeping cpus for nohz_full cpus

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  [PATCH 0/2] nohz_full: Offload task_tick to remote housekeeping cpus  for nohz_full cpus Vatika Harlalka <vatikaharlalka@gmail.com> - 2015-08-13 11:30 +0200
    [PATCH 1/2] nohz_full: Move tick related code to tick.c Vatika Harlalka <vatikaharlalka@gmail.com> - 2015-08-13 11:30 +0200
    Re: [PATCH 0/2] nohz_full: Offload task_tick to remote housekeeping  cpus for nohz_full cpus Peter Zijlstra <peterz@infradead.org> - 2015-08-13 14:30 +0200
      Re: [PATCH 0/2] nohz_full: Offload task_tick to remote housekeeping  cpus for nohz_full cpus Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-13 14:50 +0200
        Re: [PATCH 0/2] nohz_full: Offload task_tick to remote housekeeping  cpus for nohz_full cpus Peter Zijlstra <peterz@infradead.org> - 2015-08-13 17:10 +0200
          Re: [PATCH 0/2] nohz_full: Offload task_tick to remote housekeeping  cpus for nohz_full cpus Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-13 17:40 +0200
            Re: [PATCH 0/2] nohz_full: Offload task_tick to remote housekeeping  cpus for nohz_full cpus Vatika Harlalka <vatikaharlalka@gmail.com> - 2015-08-13 21:30 +0200

#1206637 — [PATCH 0/2] nohz_full: Offload task_tick to remote housekeeping cpus for nohz_full cpus

This patchset is for offloading task_tick() to a remote housekeeping
cpu. The larger aim is to stop ticks on nohz_full cpus. For this, extra
work must be done by housekeeping cpus. So, task_tick is called from a
delayed workqueue for nohz_full cpus and the work is requeued every second
for those nohz_full cpus whose ticks are stopped while they are busy. In
the rest of the cases it will lead to redundant accounting. To facilitate
this, a new function tick_nohz_remote_tick_stopped is added to indicate
whether ticks are stopped on a remote cpu.
Tick related code in core.c is moved to tick.c

Vatika Harlalka (2):
  nohz_full: Move tick related code to tick.c
  nohz_full: Offload task_tick to remote housekeeping cpu

 include/linux/tick.h     |  2 ++
 kernel/sched/Makefile    |  2 +-
 kernel/sched/core.c      | 27 ---------------
 kernel/sched/tick.c      | 85 ++++++++++++++++++++++++++++++++++++++++++++++++
 kernel/time/tick-sched.c |  5 +++
 5 files changed, 93 insertions(+), 28 deletions(-)
 create mode 100644 kernel/sched/tick.c

-- 
2.4.2

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#1206641 — [PATCH 1/2] nohz_full: Move tick related code to tick.c

Offloading task_tick off nohz_full cpus introduces tick related code
in the scheduler code. It is therefore better to create a new file
tick.c and move the existing tick related code there.

Signed-off-by: Vatika Harlalka <vatikaharlalka@gmail.com>
---
 kernel/sched/Makefile |  2 +-
 kernel/sched/core.c   | 27 ---------------------------
 kernel/sched/tick.c   | 43 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 44 insertions(+), 28 deletions(-)
 create mode 100644 kernel/sched/tick.c

diff --git a/kernel/sched/Makefile b/kernel/sched/Makefile
index 46be870..3b31182 100644
--- a/kernel/sched/Makefile
+++ b/kernel/sched/Makefile
@@ -11,7 +11,7 @@ ifneq ($(CONFIG_SCHED_OMIT_FRAME_POINTER),y)
 CFLAGS_core.o := $(PROFILING) -fno-omit-frame-pointer
 endif
 
-obj-y += core.o proc.o clock.o cputime.o
+obj-y += core.o proc.o clock.o cputime.o tick.o
 obj-y += idle_task.o fair.o rt.o deadline.o stop_task.o
 obj-y += wait.o completion.o idle.o
 obj-$(CONFIG_SMP) += cpupri.o cpudeadline.o
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 57bd333..64beceb 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2481,33 +2481,6 @@ unsigned long long task_sched_runtime(struct task_struct *p)
 	return ns;
 }
 
-/*
- * This function gets called by the timer code, with HZ frequency.
- * We call it with interrupts disabled.
- */
-void scheduler_tick(void)
-{
-	int cpu = smp_processor_id();
-	struct rq *rq = cpu_rq(cpu);
-	struct task_struct *curr = rq->curr;
-
-	sched_clock_tick();
-
-	raw_spin_lock(&rq->lock);
-	update_rq_clock(rq);
-	curr->sched_class->task_tick(rq, curr, 0);
-	update_cpu_load_active(rq);
-	raw_spin_unlock(&rq->lock);
-
-	perf_event_task_tick();
-
-#ifdef CONFIG_SMP
-	rq->idle_balance = idle_cpu(cpu);
-	trigger_load_balance(rq);
-#endif
-	rq_last_tick_reset(rq);
-}
-
 #ifdef CONFIG_NO_HZ_FULL
 /**
  * scheduler_tick_max_deferment
diff --git a/kernel/sched/tick.c b/kernel/sched/tick.c
new file mode 100644
index 0000000..3bc32c7
--- /dev/null
+++ b/kernel/sched/tick.c
@@ -0,0 +1,43 @@
+#include <linux/smp.h>
+#include <linux/cpumask.h>
+#include <linux/tick.h>
+#include <linux/sched.h>
+#include <linux/spinlock.h>
+#include <linux/percpu.h>
+#include <linux/perf_event.h>
+#include <linux/workqueue.h>
+#include <linux/jiffies.h>
+#include "sched.h"
+
+/*
+ * This function gets called by the timer code, with HZ frequency.
+ * We call it with interrupts disabled.
+ */
+
+void scheduler_tick(void)
+{
+	int cpu = smp_processor_id();
+	struct rq *rq = cpu_rq(cpu);
+	struct task_struct *curr;
+
+	raw_spin_lock(&rq->lock);
+	curr = rq->curr;
+	raw_spin_unlock(&rq->lock);
+
+	sched_clock_tick();
+
+	raw_spin_lock(&rq->lock);
+	update_rq_clock(rq);
+	curr->sched_class->task_tick(rq, curr, 0);
+	update_cpu_load_active(rq);
+	raw_spin_unlock(&rq->lock);
+
+	perf_event_task_tick();
+
+#ifdef CONFIG_SMP
+	rq->idle_balance = idle_cpu(cpu);
+	trigger_load_balance(rq);
+#endif
+	rq_last_tick_reset(rq);
+}
+
-- 
2.4.2

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#1206777 — Re: [PATCH 0/2] nohz_full: Offload task_tick to remote housekeeping cpus for nohz_full cpus

On Thu, Aug 13, 2015 at 02:55:36PM +0530, Vatika Harlalka wrote:
> This patchset is for offloading task_tick() to a remote housekeeping
> cpu. The larger aim is to stop ticks on nohz_full cpus. For this, extra
> work must be done by housekeeping cpus. So, task_tick is called from a
> delayed workqueue for nohz_full cpus and the work is requeued every second
> for those nohz_full cpus whose ticks are stopped while they are busy. In
> the rest of the cases it will lead to redundant accounting. To facilitate
> this, a new function tick_nohz_remote_tick_stopped is added to indicate
> whether ticks are stopped on a remote cpu.
> Tick related code in core.c is moved to tick.c

*sigh* of course you didn't read what I've written on this topic..
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#1206789 — Re: [PATCH 0/2] nohz_full: Offload task_tick to remote housekeeping cpus for nohz_full cpus

On Thu, Aug 13, 2015 at 02:22:23PM +0200, Peter Zijlstra wrote:
> On Thu, Aug 13, 2015 at 02:55:36PM +0530, Vatika Harlalka wrote:
> > This patchset is for offloading task_tick() to a remote housekeeping
> > cpu. The larger aim is to stop ticks on nohz_full cpus. For this, extra
> > work must be done by housekeeping cpus. So, task_tick is called from a
> > delayed workqueue for nohz_full cpus and the work is requeued every second
> > for those nohz_full cpus whose ticks are stopped while they are busy. In
> > the rest of the cases it will lead to redundant accounting. To facilitate
> > this, a new function tick_nohz_remote_tick_stopped is added to indicate
> > whether ticks are stopped on a remote cpu.
> > Tick related code in core.c is moved to tick.c
> 
> *sigh* of course you didn't read what I've written on this topic..

What is it? Note Vatika wrote this after my suggestion, so if there is an issue,
I'm likely the responsible :-) But I don't recall you opposed to this solution.

Thanks.
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#1206899 — Re: [PATCH 0/2] nohz_full: Offload task_tick to remote housekeeping cpus for nohz_full cpus

On Thu, Aug 13, 2015 at 02:44:02PM +0200, Frederic Weisbecker wrote:
> On Thu, Aug 13, 2015 at 02:22:23PM +0200, Peter Zijlstra wrote:
> > On Thu, Aug 13, 2015 at 02:55:36PM +0530, Vatika Harlalka wrote:
> > > This patchset is for offloading task_tick() to a remote housekeeping
> > > cpu. The larger aim is to stop ticks on nohz_full cpus. For this, extra
> > > work must be done by housekeeping cpus. So, task_tick is called from a
> > > delayed workqueue for nohz_full cpus and the work is requeued every second
> > > for those nohz_full cpus whose ticks are stopped while they are busy. In
> > > the rest of the cases it will lead to redundant accounting. To facilitate
> > > this, a new function tick_nohz_remote_tick_stopped is added to indicate
> > > whether ticks are stopped on a remote cpu.
> > > Tick related code in core.c is moved to tick.c
> > 
> > *sigh* of course you didn't read what I've written on this topic..
> 
> What is it? Note Vatika wrote this after my suggestion, so if there is an issue,
> I'm likely the responsible :-) But I don't recall you opposed to this solution.

*sigh* of course you _could_ all use Google yourselves.

Re-read: https://patches.linaro.org/28290/

I see nothing like the stuff I asked for in here, on top it creates the
stupid tick.c file.


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#1206924 — Re: [PATCH 0/2] nohz_full: Offload task_tick to remote housekeeping cpus for nohz_full cpus

On Thu, Aug 13, 2015 at 05:05:45PM +0200, Peter Zijlstra wrote:
> On Thu, Aug 13, 2015 at 02:44:02PM +0200, Frederic Weisbecker wrote:
> > On Thu, Aug 13, 2015 at 02:22:23PM +0200, Peter Zijlstra wrote:
> > > On Thu, Aug 13, 2015 at 02:55:36PM +0530, Vatika Harlalka wrote:
> > > > This patchset is for offloading task_tick() to a remote housekeeping
> > > > cpu. The larger aim is to stop ticks on nohz_full cpus. For this, extra
> > > > work must be done by housekeeping cpus. So, task_tick is called from a
> > > > delayed workqueue for nohz_full cpus and the work is requeued every second
> > > > for those nohz_full cpus whose ticks are stopped while they are busy. In
> > > > the rest of the cases it will lead to redundant accounting. To facilitate
> > > > this, a new function tick_nohz_remote_tick_stopped is added to indicate
> > > > whether ticks are stopped on a remote cpu.
> > > > Tick related code in core.c is moved to tick.c
> > > 
> > > *sigh* of course you didn't read what I've written on this topic..
> > 
> > What is it? Note Vatika wrote this after my suggestion, so if there is an issue,
> > I'm likely the responsible :-) But I don't recall you opposed to this solution.
> 
> *sigh* of course you _could_ all use Google yourselves.
> 
> Re-read: https://patches.linaro.org/28290/

Sorry, there were dozens of threads about this issue and I got a bit confused.

> 
> I see nothing like the stuff I asked for in here, on top it creates the
> stupid tick.c file.

Right. I initially thought that we should make sched_tick() just work with long delays.
Then tglx suggested the offline idea but I lost track about our conversation.

But yeah making that scheduler_tick() working with long delays sound much better. Certainly
much more work but that's a natural evolution after all. It should pay in longer term.

We can start with update_cpu_load_active() which only works with HZ frequency updates or
nohz idle zero load decay. Now I think that stuff is only used for load balancing. I had
hopes this thing could be removed. I think Alex Shin (IIRC) tried but the patchset didn't
make it.

Thanks.
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#1207101 — Re: [PATCH 0/2] nohz_full: Offload task_tick to remote housekeeping cpus for nohz_full cpus

Hi Peter :)

I'm very sorry about this. I should've gone through what was written
on the topic before
attempting to write this patch. I'll go through the link and work on
what is discussed
to make a new relevant patch.

Thanks
Vatika
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