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authorPaul E. McKenney <paul.mckenney@linaro.org>2012-08-19 21:35:53 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-11-16 10:05:56 -0800
commit3fbfbf7a3b66ec424042d909f14ba2ddf4372ea8 (patch)
treecc364c320a6e23927ecc154a8ef8021dc7d1a9e8 /init
parentaac1cda34b84a9411d6b8d18c3658f094c834911 (diff)
downloadlinaro-lsk-3fbfbf7a3b66ec424042d909f14ba2ddf4372ea8.tar.gz
rcu: Add callback-free CPUs
RCU callback execution can add significant OS jitter and also can degrade both scheduling latency and, in asymmetric multiprocessors, energy efficiency. This commit therefore adds the ability for selected CPUs ("rcu_nocbs=" boot parameter) to have their callbacks offloaded to kthreads. If the "rcu_nocb_poll" boot parameter is also specified, these kthreads will do polling, removing the need for the offloaded CPUs to do wakeups. At least one CPU must be doing normal callback processing: currently CPU 0 cannot be selected as a no-CBs CPU. In addition, attempts to offline the last normal-CBs CPU will fail. This feature was inspired by Jim Houston's and Joe Korty's JRCU, and this commit includes fixes to problems located by Fengguang Wu's kbuild test robot. [ paulmck: Added gfp.h include file as suggested by Fengguang Wu. ] Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'init')
-rw-r--r--init/Kconfig22
1 files changed, 22 insertions, 0 deletions
diff --git a/init/Kconfig b/init/Kconfig
index ec62139207d..5ac6ee09422 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -654,6 +654,28 @@ config RCU_BOOST_DELAY
Accept the default if unsure.
+config RCU_NOCB_CPU
+ bool "Offload RCU callback processing from boot-selected CPUs"
+ depends on TREE_RCU || TREE_PREEMPT_RCU
+ default n
+ help
+ Use this option to reduce OS jitter for aggressive HPC or
+ real-time workloads. It can also be used to offload RCU
+ callback invocation to energy-efficient CPUs in battery-powered
+ asymmetric multiprocessors.
+
+ This option offloads callback invocation from the set of
+ CPUs specified at boot time by the rcu_nocbs parameter.
+ For each such CPU, a kthread ("rcuoN") will be created to
+ invoke callbacks, where the "N" is the CPU being offloaded.
+ Nothing prevents this kthread from running on the specified
+ CPUs, but (1) the kthreads may be preempted between each
+ callback, and (2) affinity or cgroups can be used to force
+ the kthreads to run on whatever set of CPUs is desired.
+
+ Say Y here if you want reduced OS jitter on selected CPUs.
+ Say N here if you are unsure.
+
endmenu # "RCU Subsystem"
config IKCONFIG