From: "Paul E. McKenney" <paul...@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 <pau...@au1.ibm.com>
Signed-off-by: Paul E. McKenney <paul...@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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