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Commit 13cfcca0 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Set RCU CPU stall times via sysfs 



The default CONFIG_RCU_CPU_STALL_TIMEOUT value of 60 seconds has served
Linux users well for production use for quite some time.  However, for
debugging, there will be more than three minutes between subsequent
stall-warning messages.  This can be an annoyingly long wait if you
are trying to work out where the offending infinite loop is hiding.

Therefore, this commit provides a rcu_cpu_stall_timeout sysfs
parameter that may be adjusted at boot time and at runtime to speed
up debugging.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 27565d64

kernel/rcutree.c

+26 −5
Original line number Diff line number Diff line
@@ -208,8 +208,11 @@ module_param(blimit, int, 0); 
module_param(qhimark, int, 0);

module_param(qlowmark, int, 0);



int rcu_cpu_stall_suppress __read_mostly;

int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */

int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;



module_param(rcu_cpu_stall_suppress, int, 0644);

module_param(rcu_cpu_stall_timeout, int, 0644);



static void force_quiescent_state(struct rcu_state *rsp, int relaxed);

static int rcu_pending(int cpu);
@@ -645,10 +648,28 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) 
	return rcu_implicit_offline_qs(rdp);

}



static int jiffies_till_stall_check(void)

{

	int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout);



	/*

	 * Limit check must be consistent with the Kconfig limits

	 * for CONFIG_RCU_CPU_STALL_TIMEOUT.

	 */

	if (till_stall_check < 3) {

		ACCESS_ONCE(rcu_cpu_stall_timeout) = 3;

		till_stall_check = 3;

	} else if (till_stall_check > 300) {

		ACCESS_ONCE(rcu_cpu_stall_timeout) = 300;

		till_stall_check = 300;

	}

	return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;

}



static void record_gp_stall_check_time(struct rcu_state *rsp)

{

	rsp->gp_start = jiffies;

	rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_CHECK;

	rsp->jiffies_stall = jiffies + jiffies_till_stall_check();

}



static void print_other_cpu_stall(struct rcu_state *rsp)
@@ -667,7 +688,7 @@ static void print_other_cpu_stall(struct rcu_state *rsp) 
		raw_spin_unlock_irqrestore(&rnp->lock, flags);

		return;

	}

	rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK;

	rsp->jiffies_stall = jiffies + 3 * jiffies_till_stall_check() + 3;



	/*

	 * Now rat on any tasks that got kicked up to the root rcu_node
@@ -726,8 +747,8 @@ static void print_cpu_stall(struct rcu_state *rsp) 


	raw_spin_lock_irqsave(&rnp->lock, flags);

	if (ULONG_CMP_GE(jiffies, rsp->jiffies_stall))

		rsp->jiffies_stall =

			jiffies + RCU_SECONDS_TILL_STALL_RECHECK;

		rsp->jiffies_stall = jiffies +

				     3 * jiffies_till_stall_check() + 3;

	raw_spin_unlock_irqrestore(&rnp->lock, flags);



	set_need_resched();  /* kick ourselves to get things going. */

kernel/rcutree.h

+0 −6
Original line number Diff line number Diff line
@@ -314,12 +314,6 @@ struct rcu_data { 
#else

#define RCU_STALL_DELAY_DELTA	       0

#endif



#define RCU_SECONDS_TILL_STALL_CHECK   (CONFIG_RCU_CPU_STALL_TIMEOUT * HZ + \

					RCU_STALL_DELAY_DELTA)

						/* for rsp->jiffies_stall */

#define RCU_SECONDS_TILL_STALL_RECHECK (3 * RCU_SECONDS_TILL_STALL_CHECK + 30)

						/* for rsp->jiffies_stall */

#define RCU_STALL_RAT_DELAY		2	/* Allow other CPUs time */

						/*  to take at least one */

						/*  scheduling clock irq */