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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2013-04-03 22:14:11 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2013-06-10 13:44:56 -0700
commit026ad2835ce6202069e7aa0b11f5f1be4de34550 (patch)
tree2fbf39aa59eee409d892dbd99b82b31e1261f366 /kernel/rcutree.h
parent9a5739d73f9369ba1cdba3889ee4e2f87be25a46 (diff)
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op-kernel-dev-026ad2835ce6202069e7aa0b11f5f1be4de34550.tar.gz
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 <paulus@au1.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcutree.h')
-rw-r--r--kernel/rcutree.h15
1 files changed, 10 insertions, 5 deletions
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 4df5034..4a39d36 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -343,12 +343,17 @@ 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 */
+#define RCU_JIFFIES_TILL_FORCE_QS (1 + (HZ > 250) + (HZ > 500))
+ /* For jiffies_till_first_fqs and */
+ /* and jiffies_till_next_fqs. */
-#define RCU_STALL_RAT_DELAY 2 /* Allow other CPUs time */
- /* to take at least one */
- /* scheduling clock irq */
- /* before ratting on them. */
+#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 scheduling clock */
+ /* irq before ratting on them. */
#define rcu_wait(cond) \
do { \
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