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rcu: Unify boost and kthread priorities

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Rename CONFIG_RCU_BOOST_PRIO to CONFIG_RCU_KTHREAD_PRIO and use this
value for both the per-CPU kthreads (rcuc/N) and the rcu boosting
threads (rcub/n).

Also, create the module_parameter rcutree.kthread_prio to be used on
the kernel command line at boot to set a new value (rcutree.kthread_prio=N).

Signed-off-by: Clark Williams <clark.williams@gmail.com>
[ paulmck: Ported to rcu/dev, applied Paul Bolle and Peter Zijlstra feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Clark Williams
2014-09-12 21:21:09 -05:00
committed by Paul E. McKenney
parent e0775cefb5
commit 21871d7eff
5 changed files with 32 additions and 24 deletions
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23
init/Kconfig
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@@ -672,30 +672,31 @@ config RCU_BOOST
Say Y here if you are working with real-time apps or heavy loads
Say N here if you are unsure.
config RCU_BOOST_PRIO
int "Real-time priority to boost RCU readers to"
config RCU_KTHREAD_PRIO
int "Real-time priority to use for RCU worker threads"
range 1 99
depends on RCU_BOOST
default 1
help
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
This option specifies the SCHED_FIFO priority value that will be
assigned to the rcuc/n and rcub/n threads and is also the value
used for RCU_BOOST (if enabled). 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_KTHREAD_PRIO to a priority higher than the highest-priority
real-time CPU-bound application thread. The default RCU_KTHREAD_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
that CPU. In this case, you should set RCU_KTHREAD_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
the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be
set to priority 6 or higher.
Specify the real-time priority, or take the default if unsure.