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rcu: Keep invoking callbacks if CPU otherwise idle

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The rcu_do_batch() function that invokes callbacks for TREE_RCU and
TREE_PREEMPT_RCU normally throttles callback invocation to avoid degrading
scheduling latency.  However, as long as the CPU would otherwise be idle,
there is no downside to continuing to invoke any callbacks that have passed
through their grace periods.  In fact, processing such callbacks in a
timely manner has the benefit of increasing the probability that the
CPU can enter the power-saving dyntick-idle mode.

Therefore, this commit allows callback invocation to continue beyond the
preset limit as long as the scheduler does not have some other task to
run and as long as context is that of the idle task or the relevant
RCU kthread.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2011-11-29 15:57:13 -08:00 • committed by Paul E. McKenney
parent facc4e1596
commit dff1672d91
3 changed files with 19 additions and 1 deletions
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5
kernel/rcutree.c
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@ -1403,7 +1403,10 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
debug_rcu_head_unqueue(list);
__rcu_reclaim(rsp->name, list);
list = next;
if (++count >= bl)
/* Stop only if limit reached and CPU has something to do. */
if (++count >= bl &&
(need_resched() ||
(!is_idle_task(current) && !rcu_is_callbacks_kthread())))
break;
}