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rcu: Modulate grace-period slow init to normalize delay

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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: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2015-04-15 12:08:22 -07:00
parent 7d0ae8086b
commit eab128e830
1 changed files with 13 additions and 2 deletions
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15
kernel/rcu/tree.c
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@ -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);
}