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| author | Peter Zijlstra <peterz@infradead.org> | 2009-08-21 11:56:45 +0200 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2009-08-21 21:48:38 +0200 |
| commit | 3e46534547eb908c70314c173b22ae17c2e8b8e3 (patch) | |
| tree | db160d69a1280e3de965ca4b6d9afa9ebdd7ae0c | |
| parent | 94a6b8cf01c940a92f945b5fe83eb2d4cd00aefd (diff) | |
| download | lwn-3e46534547eb908c70314c173b22ae17c2e8b8e3.tar.gz lwn-3e46534547eb908c70314c173b22ae17c2e8b8e3.zip | |
timer: delay waking softirqs from the jiffy tick
People were complaining about broken balancing with the recent -rt
series.
A look at /proc/sched_debug yielded:
cpu#0, 2393.874 MHz
.nr_running : 0
.load : 0
.cpu_load[0] : 177522
.cpu_load[1] : 177522
.cpu_load[2] : 177522
.cpu_load[3] : 177522
.cpu_load[4] : 177522
cpu#1, 2393.874 MHz
.nr_running : 4
.load : 4096
.cpu_load[0] : 181618
.cpu_load[1] : 180850
.cpu_load[2] : 180274
.cpu_load[3] : 179938
.cpu_load[4] : 179758
Which indicated the cpu_load computation was hosed, the 177522 value
indicates that there is one RT task runnable. Initially I thought the
old problem of calculating the cpu_load from a softirq had re-surfaced,
however looking at the code shows its being done from scheduler_tick().
[ we really should fix this RT/cfs interaction some day... ]
A few trace_printk()s later:
sirq-timer/1-19 [001] 174.289744: 19: 50:S ==> [001] 0:140:R <idle>
<idle>-0 [001] 174.290724: enqueue_task_rt: adding task: 19/sirq-timer/1 with load: 177522
<idle>-0 [001] 174.290725: 0:140:R + [001] 19: 50:S sirq-timer/1
<idle>-0 [001] 174.290730: scheduler_tick: current load: 177522
<idle>-0 [001] 174.290732: scheduler_tick: current: 0/swapper
<idle>-0 [001] 174.290736: 0:140:R ==> [001] 19: 50:R sirq-timer/1
sirq-timer/1-19 [001] 174.290741: dequeue_task_rt: removing task: 19/sirq-timer/1 with load: 177522
sirq-timer/1-19 [001] 174.290743: 19: 50:S ==> [001] 0:140:R <idle>
We see that we always raise the timer softirq before doing the load
calculation. Avoid this by re-ordering the scheduler_tick() call in
update_process_times() to occur before we deal with timers.
This lowers the load back to sanity and restores regular load-balancing
behaviour.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
| -rw-r--r-- | kernel/timer.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/timer.c b/kernel/timer.c index 8137cce92a2b..96ac1b4d7035 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -1221,10 +1221,10 @@ void update_process_times(int user_tick) /* Note: this timer irq context must be accounted for as well. */ account_process_tick(p, user_tick); + scheduler_tick(); run_local_timers(); if (rcu_pending(cpu)) rcu_check_callbacks(cpu, user_tick); - scheduler_tick(); run_posix_cpu_timers(p); } |