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authorSteven Rostedt <rostedt@goodmis.org>2008-07-07 14:16:52 -0400
committerIngo Molnar <mingo@elte.hu>2008-07-11 09:53:26 -0400
commitaf52a90a14cdaa54ecbfb6e6982abb13466a4b56 (patch)
tree2488d6d7943b167987c33f984f7109c3dc4ae783 /kernel/time/tick-sched.c
parentf7cce27f5605b9e137b829a47949cb2d3c7e1cab (diff)
sched_clock: stop maximum check on NO HZ
Working with ftrace I would get large jumps of 11 millisecs or more with the clock tracer. This killed the latencing timings of ftrace and also caused the irqoff self tests to fail. What was happening is with NO_HZ the idle would stop the jiffy counter and before the jiffy counter was updated the sched_clock would have a bad delta jiffies to compare with the gtod with the maximum. The jiffies would stop and the last sched_tick would record the last gtod. On wakeup, the sched clock update would compare the gtod + delta jiffies (which would be zero) and compare it to the TSC. The TSC would have correctly (with a stable TSC) moved forward several jiffies. But because the jiffies has not been updated yet the clock would be prevented from moving forward because it would appear that the TSC jumped too far ahead. The clock would then virtually stop, until the jiffies are updated. Then the next sched clock update would see that the clock was very much behind since the delta jiffies is now correct. This would then jump the clock forward by several jiffies. This caused ftrace to report several milliseconds of interrupts off latency at every resume from NO_HZ idle. This patch adds hooks into the nohz code to disable the checking of the maximum clock update when nohz is in effect. It resumes the max check when nohz has updated the jiffies again. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Cc: Steven Rostedt <srostedt@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/time/tick-sched.c')
-rw-r--r--kernel/time/tick-sched.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index b854a895591e..d63008b09a4c 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -276,6 +276,7 @@ void tick_nohz_stop_sched_tick(void)
276 ts->tick_stopped = 1; 276 ts->tick_stopped = 1;
277 ts->idle_jiffies = last_jiffies; 277 ts->idle_jiffies = last_jiffies;
278 rcu_enter_nohz(); 278 rcu_enter_nohz();
279 sched_clock_tick_stop(cpu);
279 } 280 }
280 281
281 /* 282 /*
@@ -375,6 +376,7 @@ void tick_nohz_restart_sched_tick(void)
375 select_nohz_load_balancer(0); 376 select_nohz_load_balancer(0);
376 now = ktime_get(); 377 now = ktime_get();
377 tick_do_update_jiffies64(now); 378 tick_do_update_jiffies64(now);
379 sched_clock_tick_start(cpu);
378 cpu_clear(cpu, nohz_cpu_mask); 380 cpu_clear(cpu, nohz_cpu_mask);
379 381
380 /* 382 /*