81 lines
3.0 KiB
Diff
81 lines
3.0 KiB
Diff
From a9235b7a3e0b3d7ca3874f88940b056df7d4088a Mon Sep 17 00:00:00 2001
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From: Peter Zijlstra <peterz@infradead.org>
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Date: Fri, 21 Aug 2009 11:56:45 +0200
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Subject: [PATCH 119/365] timer: delay waking softirqs from the jiffy tick
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People were complaining about broken balancing with the recent -rt
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series.
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A look at /proc/sched_debug yielded:
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cpu#0, 2393.874 MHz
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.nr_running : 0
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.load : 0
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.cpu_load[0] : 177522
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.cpu_load[1] : 177522
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.cpu_load[2] : 177522
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.cpu_load[3] : 177522
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.cpu_load[4] : 177522
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cpu#1, 2393.874 MHz
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.nr_running : 4
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.load : 4096
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.cpu_load[0] : 181618
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.cpu_load[1] : 180850
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.cpu_load[2] : 180274
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.cpu_load[3] : 179938
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.cpu_load[4] : 179758
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Which indicated the cpu_load computation was hosed, the 177522 value
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indicates that there is one RT task runnable. Initially I thought the
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old problem of calculating the cpu_load from a softirq had re-surfaced,
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however looking at the code shows its being done from scheduler_tick().
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[ we really should fix this RT/cfs interaction some day... ]
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A few trace_printk()s later:
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sirq-timer/1-19 [001] 174.289744: 19: 50:S ==> [001] 0:140:R <idle>
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<idle>-0 [001] 174.290724: enqueue_task_rt: adding task: 19/sirq-timer/1 with load: 177522
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<idle>-0 [001] 174.290725: 0:140:R + [001] 19: 50:S sirq-timer/1
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<idle>-0 [001] 174.290730: scheduler_tick: current load: 177522
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<idle>-0 [001] 174.290732: scheduler_tick: current: 0/swapper
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<idle>-0 [001] 174.290736: 0:140:R ==> [001] 19: 50:R sirq-timer/1
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sirq-timer/1-19 [001] 174.290741: dequeue_task_rt: removing task: 19/sirq-timer/1 with load: 177522
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sirq-timer/1-19 [001] 174.290743: 19: 50:S ==> [001] 0:140:R <idle>
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We see that we always raise the timer softirq before doing the load
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calculation. Avoid this by re-ordering the scheduler_tick() call in
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update_process_times() to occur before we deal with timers.
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This lowers the load back to sanity and restores regular load-balancing
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behaviour.
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Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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---
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kernel/time/timer.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/kernel/time/timer.c b/kernel/time/timer.c
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index 1a7b5f87a006..4686736fc986 100644
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--- a/kernel/time/timer.c
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+++ b/kernel/time/timer.c
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@@ -1661,13 +1661,13 @@ void update_process_times(int user_tick)
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/* Note: this timer irq context must be accounted for as well. */
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account_process_tick(p, user_tick);
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+ scheduler_tick();
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run_local_timers();
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rcu_check_callbacks(user_tick);
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#ifdef CONFIG_IRQ_WORK
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if (in_irq())
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irq_work_tick();
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#endif
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- scheduler_tick();
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run_posix_cpu_timers(p);
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}
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--
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2.28.0
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