Commit eab128e8 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Modulate grace-period slow init to normalize delay 



Currently, the larger the gp_init_delay boot parameter, the slower
rcutorture will sequence through grace periods.  This commit avoids this
issue by decreasing the probability of slowing initialization of a given
grace period as the degree of slowness increases.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 7d0ae808

kernel/rcu/tree.c

+13 −2
Original line number Diff line number Diff line
@@ -169,7 +169,17 @@ module_param(gp_init_delay, int, 0644); 
#else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */

static const int gp_init_delay;

#endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */

#define PER_RCU_NODE_PERIOD 10	/* Number of grace periods between delays. */



/*

 * Number of grace periods between delays, normalized by the duration of

 * the delay.  The longer the the delay, the more the grace periods between

 * each delay.  The reason for this normalization is that it means that,

 * for non-zero delays, the overall slowdown of grace periods is constant

 * regardless of the duration of the delay.  This arrangement balances

 * the need for long delays to increase some race probabilities with the

 * need for fast grace periods to increase other race probabilities.

 */

#define PER_RCU_NODE_PERIOD 3	/* Number of grace periods between delays. */



/*

 * Track the rcutorture test sequence number and the update version
@@ -1848,7 +1858,8 @@ static int rcu_gp_init(struct rcu_state *rsp) 
		cond_resched_rcu_qs();

		WRITE_ONCE(rsp->gp_activity, jiffies);

		if (gp_init_delay > 0 &&

		    !(rsp->gpnum % (rcu_num_nodes * PER_RCU_NODE_PERIOD)))

		    !(rsp->gpnum %

		      (rcu_num_nodes * PER_RCU_NODE_PERIOD * gp_init_delay)))

			schedule_timeout_uninterruptible(gp_init_delay);

	}