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rcu: Provide cond_resched_rcu_qs() to force quiescent states in long loops

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RCU-tasks requires the occasional voluntary context switch
from CPU-bound in-kernel tasks.  In some cases, this requires
instrumenting cond_resched().  However, there is some reluctance
to countenance unconditionally instrumenting cond_resched() (see
http://lwn.net/Articles/603252/), so this commit creates a separate
cond_resched_rcu_qs() that may be used in place of cond_resched() in
locations prone to long-duration in-kernel looping.

This commit currently instruments only RCU-tasks.  Future possibilities
include also instrumenting RCU, RCU-bh, and RCU-sched in order to reduce
IPI usage.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney
2014-07-01 11:26:57 -07:00
parent 8315f42295
commit bde6c3aa99
6 changed files with 24 additions and 11 deletions
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4
kernel/rcu/rcutorture.c
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@@ -667,7 +667,7 @@ static int rcu_torture_boost(void *arg)
}
call_rcu_time = jiffies;
}
cond_resched();
cond_resched_rcu_qs();
stutter_wait("rcu_torture_boost");
if (torture_must_stop())
goto checkwait;
@@ -1019,7 +1019,7 @@ rcu_torture_reader(void *arg)
__this_cpu_inc(rcu_torture_batch[completed]);
preempt_enable();
cur_ops->readunlock(idx);
cond_resched();
cond_resched_rcu_qs();
stutter_wait("rcu_torture_reader");
} while (!torture_must_stop());
if (irqreader && cur_ops->irq_capable) {