rcu: Make RCU_FAST_NO_HZ take advantage of numbered callbacks
Because RCU callbacks are now associated with the number of the grace
period that they must wait for, CPUs can now take advance callbacks
corresponding to grace periods that ended while a given CPU was in
dyntick-idle mode. This eliminates the need to try forcing the RCU
state machine while entering idle, thus reducing the CPU intensiveness
of RCU_FAST_NO_HZ, which should increase its energy efficiency.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index a17ba16..22303b2 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2490,6 +2490,17 @@
leaf rcu_node structure. Useful for very large
systems.
+ rcutree.jiffies_till_first_fqs= [KNL,BOOT]
+ Set delay from grace-period initialization to
+ first attempt to force quiescent states.
+ Units are jiffies, minimum value is zero,
+ and maximum value is HZ.
+
+ rcutree.jiffies_till_next_fqs= [KNL,BOOT]
+ Set delay between subsequent attempts to force
+ quiescent states. Units are jiffies, minimum
+ value is one, and maximum value is HZ.
+
rcutree.qhimark= [KNL,BOOT]
Set threshold of queued
RCU callbacks over which batch limiting is disabled.
@@ -2504,16 +2515,15 @@
rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
Set timeout for RCU CPU stall warning messages.
- rcutree.jiffies_till_first_fqs= [KNL,BOOT]
- Set delay from grace-period initialization to
- first attempt to force quiescent states.
- Units are jiffies, minimum value is zero,
- and maximum value is HZ.
+ rcutree.rcu_idle_gp_delay= [KNL,BOOT]
+ Set wakeup interval for idle CPUs that have
+ RCU callbacks (RCU_FAST_NO_HZ=y).
- rcutree.jiffies_till_next_fqs= [KNL,BOOT]
- Set delay between subsequent attempts to force
- quiescent states. Units are jiffies, minimum
- value is one, and maximum value is HZ.
+ rcutree.rcu_idle_lazy_gp_delay= [KNL,BOOT]
+ Set wakeup interval for idle CPUs that have
+ only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
+ Lazy RCU callbacks are those which RCU can
+ prove do nothing more than free memory.
rcutorture.fqs_duration= [KNL,BOOT]
Set duration of force_quiescent_state bursts.