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authorPaul E. McKenney <paul.mckenney@linaro.org>2012-04-18 16:20:18 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-04-24 20:54:50 -0700
commitc9336643e1440f4dfc89ad4ac6185813619abb8c (patch)
tree1a32e3f08548a4b55cd2ec93b240c11a361e74ca /init/Kconfig
parentf88022a4f650ac1778cafcc17d2e522283bdf590 (diff)
downloadlinux-linaro-stable-c9336643e1440f4dfc89ad4ac6185813619abb8c.tar.gz
rcu: Clarify help text for RCU_BOOST_PRIO
The old text confused real-time applications with real-time threads, so that you pretty much needed to understand how this kernel configuration parameter worked to understand the help text. This commit therefore attempts to make the help text human-readable. Reported-by: Jörn Engel <joern@purestorage.com> 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/Kconfig')
-rw-r--r--init/Kconfig23
1 files changed, 19 insertions, 4 deletions
diff --git a/init/Kconfig b/init/Kconfig
index 6cfd71d06463..85c6870ed476 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -515,10 +515,25 @@ config RCU_BOOST_PRIO
depends on RCU_BOOST
default 1
help
- This option specifies the real-time priority to which preempted
- RCU readers are to be boosted. If you are working with CPU-bound
- real-time applications, you should specify a priority higher then
- the highest-priority CPU-bound application.
+ This option specifies the real-time priority to which long-term
+ preempted RCU readers are to be boosted. If you are working
+ with a real-time application that has one or more CPU-bound
+ threads running at a real-time priority level, you should set
+ RCU_BOOST_PRIO to a priority higher then the highest-priority
+ real-time CPU-bound thread. The default RCU_BOOST_PRIO value
+ of 1 is appropriate in the common case, which is real-time
+ applications that do not have any CPU-bound threads.
+
+ Some real-time applications might not have a single real-time
+ thread that saturates a given CPU, but instead might have
+ multiple real-time threads that, taken together, fully utilize
+ that CPU. In this case, you should set RCU_BOOST_PRIO to
+ a priority higher than the lowest-priority thread that is
+ conspiring to prevent the CPU from running any non-real-time
+ tasks. For example, if one thread at priority 10 and another
+ thread at priority 5 are between themselves fully consuming
+ the CPU time on a given CPU, then RCU_BOOST_PRIO should be
+ set to priority 6 or higher.
Specify the real-time priority, or take the default if unsure.