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authorThomas Gleixner <tglx@linutronix.de>2009-04-11 10:43:41 +0200
committerThomas Gleixner <tglx@linutronix.de>2009-05-15 15:32:45 +0200
commitdce48a84adf1806676319f6f480e30a6daa012f9 (patch)
tree79151f5d31d9c3dcdc723ab8877cb943b944890e /kernel/timer.c
parent2ff799d3cff1ecb274049378b28120ee5c1c5e5f (diff)
downloadlinux-dce48a84adf1806676319f6f480e30a6daa012f9.tar.bz2
sched, timers: move calc_load() to scheduler
Dimitri Sivanich noticed that xtime_lock is held write locked across calc_load() which iterates over all online CPUs. That can cause long latencies for xtime_lock readers on large SMP systems. The load average calculation is an rough estimate anyway so there is no real need to protect the readers vs. the update. It's not a problem when the avenrun array is updated while a reader copies the values. Instead of iterating over all online CPUs let the scheduler_tick code update the number of active tasks shortly before the avenrun update happens. The avenrun update itself is handled by the CPU which calls do_timer(). [ Impact: reduce xtime_lock write locked section ] Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra <peterz@infradead.org>
Diffstat (limited to 'kernel/timer.c')
-rw-r--r--kernel/timer.c54
1 files changed, 2 insertions, 52 deletions
diff --git a/kernel/timer.c b/kernel/timer.c
index cffffad01c31..6a21d7af9620 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1123,47 +1123,6 @@ void update_process_times(int user_tick)
}
/*
- * Nr of active tasks - counted in fixed-point numbers
- */
-static unsigned long count_active_tasks(void)
-{
- return nr_active() * FIXED_1;
-}
-
-/*
- * Hmm.. Changed this, as the GNU make sources (load.c) seems to
- * imply that avenrun[] is the standard name for this kind of thing.
- * Nothing else seems to be standardized: the fractional size etc
- * all seem to differ on different machines.
- *
- * Requires xtime_lock to access.
- */
-unsigned long avenrun[3];
-
-EXPORT_SYMBOL(avenrun);
-
-/*
- * calc_load - given tick count, update the avenrun load estimates.
- * This is called while holding a write_lock on xtime_lock.
- */
-static inline void calc_load(unsigned long ticks)
-{
- unsigned long active_tasks; /* fixed-point */
- static int count = LOAD_FREQ;
-
- count -= ticks;
- if (unlikely(count < 0)) {
- active_tasks = count_active_tasks();
- do {
- CALC_LOAD(avenrun[0], EXP_1, active_tasks);
- CALC_LOAD(avenrun[1], EXP_5, active_tasks);
- CALC_LOAD(avenrun[2], EXP_15, active_tasks);
- count += LOAD_FREQ;
- } while (count < 0);
- }
-}
-
-/*
* This function runs timers and the timer-tq in bottom half context.
*/
static void run_timer_softirq(struct softirq_action *h)
@@ -1187,16 +1146,6 @@ void run_local_timers(void)
}
/*
- * Called by the timer interrupt. xtime_lock must already be taken
- * by the timer IRQ!
- */
-static inline void update_times(unsigned long ticks)
-{
- update_wall_time();
- calc_load(ticks);
-}
-
-/*
* The 64-bit jiffies value is not atomic - you MUST NOT read it
* without sampling the sequence number in xtime_lock.
* jiffies is defined in the linker script...
@@ -1205,7 +1154,8 @@ static inline void update_times(unsigned long ticks)
void do_timer(unsigned long ticks)
{
jiffies_64 += ticks;
- update_times(ticks);
+ update_wall_time();
+ calc_global_load();
}
#ifdef __ARCH_WANT_SYS_ALARM