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

From: Yong Zhang
Date: Wed Jan 26 2011 - 00:56:42 EST


On Tue, Jan 25, 2011 at 05:51:59PM +0100, Peter Zijlstra wrote:
> On Tue, 2011-01-25 at 11:34 +0100, Peter Zijlstra wrote:
>
> > Something like the (completely untested) below would do I guess:
>
> > @@ -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:
>
> OK, so calling mod_timer() before init_timers() is _not_ a good idea ;-)

So I change your patch a little, and it works well on my PC ;)

0) move calc_global_times things to one function start_calc_global_timer();
1) call start_calc_global_timer() in sched_init_smp() instead of
sched_init(); thus we change the boot-time load calculation(later
than before), but I don't think it's matter;
2) remove timer_before() check in calc_global_load(), if that check
returns true, we will lose global-load-timer forever.

Thanks,
Yong

---
From: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Subject: [PATCH] sched: Move the calc_global_load() call into the scheduler

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>
Signed-off-by: Yong Zhang <yong.zhang0@xxxxxxxxx>
---
include/linux/sched.h | 2 --
kernel/sched.c | 34 +++++++++++++++++++++++-----------
kernel/timer.c | 1 -
3 files changed, 23 insertions(+), 14 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d747f94..f224dcc 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -142,8 +142,6 @@ extern unsigned long nr_iowait_cpu(int cpu);
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;
diff --git a/kernel/sched.c b/kernel/sched.c
index 18d38e4..89f6725 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3159,7 +3159,7 @@ calc_load_n(unsigned long load, unsigned long exp,
* 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;

@@ -3179,8 +3179,9 @@ static void calc_global_nohz(unsigned long ticks)
/*
* 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;
@@ -3213,7 +3214,7 @@ static inline long calc_load_fold_idle(void)
return 0;
}

-static void calc_global_nohz(unsigned long ticks)
+static void calc_global_nohz(void)
{
}
#endif
@@ -3233,18 +3234,27 @@ void get_avenrun(unsigned long *loads, unsigned long offset, int shift)
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);
+
+static __init void start_calc_global_timer()
+{
+ calc_load_update = jiffies + LOAD_FREQ;
+ set_timer_slack(&global_load_timer, 0);
+ mod_timer(&global_load_timer, calc_load_update + 10);
+}
+
/*
* 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);
-
- if (time_before(jiffies, calc_load_update + 10))
- return;
+ calc_global_nohz();

active = atomic_long_read(&calc_load_tasks);
active = active > 0 ? active * FIXED_1 : 0;
@@ -3254,6 +3264,7 @@ void calc_global_load(unsigned long ticks)
avenrun[2] = calc_load(avenrun[2], EXP_15, active);

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

/*
@@ -7741,6 +7752,8 @@ void __init sched_init_smp(void)
{
cpumask_var_t non_isolated_cpus;

+ start_calc_global_timer();
+
alloc_cpumask_var(&non_isolated_cpus, GFP_KERNEL);
alloc_cpumask_var(&fallback_doms, GFP_KERNEL);

@@ -7777,6 +7790,7 @@ void __init sched_init_smp(void)
#else
void __init sched_init_smp(void)
{
+ start_calc_global_timer();
sched_init_granularity();
}
#endif /* CONFIG_SMP */
@@ -8044,8 +8058,6 @@ void __init sched_init(void)
*/
init_idle(current, smp_processor_id());

- calc_load_update = jiffies + LOAD_FREQ;
-
/*
* During early bootup we pretend to be a normal task:
*/
diff --git a/kernel/timer.c b/kernel/timer.c
index 43ca993..afdc13b 100644
--- a/kernel/timer.c
+++ b/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
--
1.7.0.4

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