summaryrefslogtreecommitdiff
path: root/kernel/rcu/Kconfig
diff options
context:
space:
mode:
authorNeeraj Upadhyay <neeraju@codeaurora.org>2020-09-24 12:04:10 +0530
committerPaul E. McKenney <paulmck@kernel.org>2020-11-19 19:37:16 -0800
commita3941517fcd6625adc540aef5ec3f717c8fa71e8 (patch)
tree53c588412fce5e39eec6dfd1fb022297c236c71c /kernel/rcu/Kconfig
parented73860cecc3ec12aa50a6dcfb4900e5b4ae9507 (diff)
rcu: Clarify nocb kthreads naming in RCU_NOCB_CPU config
This commit clarifies that the "p" and the "s" in the in the RCU_NOCB_CPU config-option description refer to the "x" in the "rcuox/N" kthread name. Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org> [ paulmck: While in the area, update description and advice. ] Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu/Kconfig')
-rw-r--r--kernel/rcu/Kconfig20
1 files changed, 12 insertions, 8 deletions
diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
index b71e21f73c40..cdc57b4f6d48 100644
--- a/kernel/rcu/Kconfig
+++ b/kernel/rcu/Kconfig
@@ -221,19 +221,23 @@ config RCU_NOCB_CPU
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.
+ asymmetric multiprocessors. The price of this reduced jitter
+ is that the overhead of call_rcu() increases and that some
+ workloads will incur significant increases in context-switch
+ rates.
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 ("rcuox/N") will be created to invoke
callbacks, where the "N" is the CPU being offloaded, and where
- the "p" for RCU-preempt (PREEMPTION kernels) and "s" for RCU-sched
- (!PREEMPTION kernels). 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 to help to debug reduced OS jitter.
+ the "x" is "p" for RCU-preempt (PREEMPTION kernels) and "s" for
+ RCU-sched (!PREEMPTION kernels). 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 need reduced OS jitter, despite added overhead.
Say N here if you are unsure.
config TASKS_TRACE_RCU_READ_MB