Re: [PATCH 01/18] move do_timer() from kernel/timer.c intokernel/time/timekeeping.c

From: Peter Zijlstra
Date: Tue Jan 25 2011 - 05:34:00 EST


On Tue, 2011-01-25 at 10:08 +0100, Peter Zijlstra wrote:
> On Mon, 2011-01-24 at 23:44 +0100, Thomas Gleixner wrote:
> > On Mon, 24 Jan 2011, Peter Zijlstra wrote:
> >
> > > On Mon, 2011-01-24 at 23:10 +0100, Thomas Gleixner wrote:
> > > > The call to calc_global_load() is there for hysterical raisins and we
> > > > really should get rid of it sooner than later. I'm quite sure that it
> > > > could be run from a timer callback as well. Peter ?
> > >
> > > calc_global_load() wants to be called on just one cpu, do we have a
> > > better place for that?
> >
> > Well, we can call it from a timer from a single CPU.
>
> Right that would work I guess.

Something like the (completely untested) below would do I guess:

---
Subject: sched: Move the calc_global_load() call into the scheduler
From: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Date: Tue Jan 25 11:30:35 CET 2011

Remove the calc_global_load() call from the timekeeping code and make
it local to the scheduler.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
LKML-Reference: <new-submission>
---
include/linux/sched.h | 2 --
kernel/sched.c | 22 ++++++++++++++++------
kernel/timer.c | 1 -
3 files changed, 16 insertions(+), 9 deletions(-)

Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -142,8 +142,6 @@ extern unsigned long nr_iowait_cpu(int c
extern unsigned long this_cpu_load(void);


-extern void calc_global_load(unsigned long ticks);
-
extern unsigned long get_parent_ip(unsigned long addr);

struct seq_file;
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -3192,7 +3192,7 @@ calc_load_n(unsigned long load, unsigned
* Once we've updated the global active value, we need to apply the exponential
* weights adjusted to the number of cycles missed.
*/
-static void calc_global_nohz(unsigned long ticks)
+static void calc_global_nohz(void)
{
long delta, active, n;

@@ -3209,11 +3209,13 @@ static void calc_global_nohz(unsigned lo
if (delta)
atomic_long_add(delta, &calc_load_tasks);

+
/*
* If we were idle for multiple load cycles, apply them.
*/
- if (ticks >= LOAD_FREQ) {
- n = ticks / LOAD_FREQ;
+ delta = jiffies - calc_load_update - 10;
+ if (delta >= LOAD_FREQ) {
+ n = delta / LOAD_FREQ;

active = atomic_long_read(&calc_load_tasks);
active = active > 0 ? active * FIXED_1 : 0;
@@ -3246,7 +3248,7 @@ static inline long calc_load_fold_idle(v
return 0;
}

-static void calc_global_nohz(unsigned long ticks)
+static void calc_global_nohz(void)
{
}
#endif
@@ -3266,15 +3268,20 @@ void get_avenrun(unsigned long *loads, u
loads[2] = (avenrun[2] + offset) << shift;
}

+static void calc_global_load(unsigned long __data);
+
+static struct timer_list global_load_timer =
+ TIMER_DEFERRED_INITIALIZER(calc_global_load, 0, 0);
+
/*
* calc_load - update the avenrun load estimates 10 ticks after the
* CPUs have updated calc_load_tasks.
*/
-void calc_global_load(unsigned long ticks)
+static void calc_global_load(unsigned long __data)
{
long active;

- calc_global_nohz(ticks);
+ calc_global_nohz();

if (time_before(jiffies, calc_load_update + 10))
return;
@@ -3287,6 +3294,7 @@ void calc_global_load(unsigned long tick
avenrun[2] = calc_load(avenrun[2], EXP_15, active);

calc_load_update += LOAD_FREQ;
+ mod_timer(&global_load_timer, calc_load_update + 10);
}

/*
@@ -8172,6 +8180,8 @@ void __init sched_init(void)
init_idle(current, smp_processor_id());

calc_load_update = jiffies + LOAD_FREQ;
+ global_load_timer.slack = 0;
+ mod_timer(&global_load_timer, calc_load_update + 10);

/*
* During early bootup we pretend to be a normal task:
Index: linux-2.6/kernel/timer.c
===================================================================
--- linux-2.6.orig/kernel/timer.c
+++ linux-2.6/kernel/timer.c
@@ -1303,7 +1303,6 @@ void do_timer(unsigned long ticks)
{
jiffies_64 += ticks;
update_wall_time();
- calc_global_load(ticks);
}

#ifdef __ARCH_WANT_SYS_ALARM

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