From 026ad2835ce6202069e7aa0b11f5f1be4de34550 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 3 Apr 2013 22:14:11 -0700 Subject: rcu: Drive quiescent-state-forcing delay from HZ Systems with HZ=100 can have slow bootup times due to the default three-jiffy delays between quiescent-state forcing attempts. This commit therefore auto-tunes the RCU_JIFFIES_TILL_FORCE_QS value based on the value of HZ. However, this would break very large systems that require more time between quiescent-state forcing attempts. This commit therefore also ups the default delay by one jiffy for each 256 CPUs that might be on the system (based off of nr_cpu_ids at runtime, -not- NR_CPUS at build time). Updated to collapse #ifdefs for RCU_JIFFIES_TILL_FORCE_QS into a step-function definition as suggested by Josh Triplett. Reported-by: Paul Mackerras Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) (limited to 'kernel/rcutree.c') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 1009c0ccd4b1..f344d3c824a4 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -218,8 +218,8 @@ module_param(blimit, long, 0444); module_param(qhimark, long, 0444); module_param(qlowmark, long, 0444); -static ulong jiffies_till_first_fqs = RCU_JIFFIES_TILL_FORCE_QS; -static ulong jiffies_till_next_fqs = RCU_JIFFIES_TILL_FORCE_QS; +static ulong jiffies_till_first_fqs = ULONG_MAX; +static ulong jiffies_till_next_fqs = ULONG_MAX; module_param(jiffies_till_first_fqs, ulong, 0644); module_param(jiffies_till_next_fqs, ulong, 0644); @@ -3265,11 +3265,25 @@ static void __init rcu_init_one(struct rcu_state *rsp, */ static void __init rcu_init_geometry(void) { + ulong d; int i; int j; int n = nr_cpu_ids; int rcu_capacity[MAX_RCU_LVLS + 1]; + /* + * Initialize any unspecified boot parameters. + * The default values of jiffies_till_first_fqs and + * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS + * value, which is a function of HZ, then adding one for each + * RCU_JIFFIES_FQS_DIV CPUs that might be on the system. + */ + d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV; + if (jiffies_till_first_fqs == ULONG_MAX) + jiffies_till_first_fqs = d; + if (jiffies_till_next_fqs == ULONG_MAX) + jiffies_till_next_fqs = d; + /* If the compile-time values are accurate, just leave. */ if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF && nr_cpu_ids == NR_CPUS) -- cgit v1.2.3-59-g8ed1b