Messages in this thread Patch in this message | | | From | "Paul E. McKenney" <> | Subject | [PATCH tip/core/rcu 6/7] rcu: Drive quiescent-state-forcing delay from HZ | Date | Fri, 12 Apr 2013 16:19:13 -0700 |
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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
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).
Reported-by: Paul Mackerras <paulus@au1.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> --- kernel/rcutree.c | 18 ++++++++++++++++-- kernel/rcutree.h | 12 +++++++++++- 2 files changed, 27 insertions(+), 3 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 3710d74..cbfb4ee 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); @@ -3252,11 +3252,25 @@ 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) diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 08972c9..7d5f876 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -342,7 +342,17 @@ struct rcu_data { #define RCU_FORCE_QS 3 /* Need to force quiescent state. */ #define RCU_SIGNAL_INIT RCU_SAVE_DYNTICK -#define RCU_JIFFIES_TILL_FORCE_QS 3 /* for rsp->jiffies_force_qs */ +#if HZ > 500 +#define RCU_JIFFIES_TILL_FORCE_QS 3 /* for jiffies_till_first_fqs */ +#elif HZ > 250 +#define RCU_JIFFIES_TILL_FORCE_QS 2 +#else +#define RCU_JIFFIES_TILL_FORCE_QS 1 +#endif +#define RCU_JIFFIES_FQS_DIV 256 /* Very large systems need */ + /* more delay between bouts */ + /* of quiescent-state */ + /* forcing. */ #define RCU_STALL_RAT_DELAY 2 /* Allow other CPUs time */ /* to take at least one */ -- 1.8.1.5
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