rcu: increment quiescent state counter in ksoftirqd()
Eric Dumazet [Wed, 4 Mar 2009 20:11:56 +0000 (12:11 -0800)]
If a machine is flooded by network frames, a cpu can loop
100% of its time inside ksoftirqd() without calling schedule().
This can delay RCU grace period to insane values.

Adding rcu_qsctr_inc() call in ksoftirqd() solves this problem.

Paul: "This regression was a result of the recent change from
"schedule()" to "cond_resched()", which got rid of that quiescent
state in the common case where a reschedule is not needed".

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/softirq.c

index bdbe9de..9041ea7 100644 (file)
@@ -626,6 +626,7 @@ static int ksoftirqd(void * __bind_cpu)
                        preempt_enable_no_resched();
                        cond_resched();
                        preempt_disable();
+                       rcu_qsctr_inc((long)__bind_cpu);
                }
                preempt_enable();
                set_current_state(TASK_INTERRUPTIBLE);