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sched clock: revert various sched_clock() changes

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Found an interactivity problem on a quad core test-system - simple
CPU loops would occasionally delay the system un an unacceptable way.

After much debugging with Peter Zijlstra it turned out that the problem
is caused by the string of sched_clock() changes - they caused the CPU
clock to jump backwards a bit - which confuses the scheduler arithmetics.

(which is unsigned for performance reasons)

So revert:

 # c300ba2: sched_clock: and multiplier for TSC to gtod drift
 # c0c8773: sched_clock: only update deltas with local reads.
 # af52a90: sched_clock: stop maximum check on NO HZ
 # f7cce27: sched_clock: widen the max and min time

This solves the interactivity problems.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Mike Galbraith <efault@gmx.de>
This commit is contained in:
Ingo Molnar 2008-04-14 08:50:02 +02:00
parent 39675e89fb
commit e4e4e534fa
3 changed files with 14 additions and 114 deletions
Download patch file Download diff file Expand all files Collapse all files

2
kernel/time/tick-sched.c
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@ -289,7 +289,6 @@ void tick_nohz_stop_sched_tick(int inidle)
ts->tick_stopped = 1;
ts->idle_jiffies = last_jiffies;
rcu_enter_nohz();
sched_clock_tick_stop(cpu);
}
/*
@ -392,7 +391,6 @@ void tick_nohz_restart_sched_tick(void)
select_nohz_load_balancer(0);
now = ktime_get();
tick_do_update_jiffies64(now);
sched_clock_tick_start(cpu);
cpu_clear(cpu, nohz_cpu_mask);
/*