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| author | Ingo Molnar <mingo@kernel.org> | 2013-04-26 10:05:59 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2013-04-26 10:13:42 +0200 |
| commit | 47aa8b6cbcb839efe2edaa5b50fee21df115d37b (patch) | |
| tree | b3c54811c75f40c11ba4344b8089156724d5e074 | |
| parent | nohz: Remove full dynticks' superfluous dependency on RCU tree (diff) | |
| download | linux-47aa8b6cbcb839efe2edaa5b50fee21df115d37b.tar.xz linux-47aa8b6cbcb839efe2edaa5b50fee21df115d37b.zip | |
nohz: Reduce overhead under high-freq idling patterns
One testbox of mine (Intel Nehalem, 16-way) uses MWAIT for its idle routine,
which apparently can break out of its idle loop rather frequently, with
high frequency.
In that case NO_HZ_FULL=y kernels show high ksoftirqd overhead and constant
context switching, because tick_nohz_stop_sched_tick() will, if
delta_jiffies == 0, mis-identify this as a timer event - activating the
TIMER_SOFTIRQ, which wakes up ksoftirqd.
Fix this by treating delta_jiffies == 0 the same way we treat other short
wakeups, delta_jiffies == 1.
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
| -rw-r--r-- | kernel/time/tick-sched.c | 7 |
1 files changed, 4 insertions, 3 deletions
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 85e05ab98253..da53c8f2beb5 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -565,11 +565,12 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, delta_jiffies = rcu_delta_jiffies; } } + /* - * Do not stop the tick, if we are only one off - * or if the cpu is required for rcu + * Do not stop the tick, if we are only one off (or less) + * or if the cpu is required for RCU: */ - if (!ts->tick_stopped && delta_jiffies == 1) + if (!ts->tick_stopped && delta_jiffies <= 1) goto out; /* Schedule the tick, if we are at least one jiffie off */ |