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rcu: Clarify nocb kthreads naming in RCU_NOCB_CPU config

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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>
This commit is contained in:
Neeraj Upadhyay 2020-09-24 12:04:10 +05:30 committed by Paul E. McKenney
parent ed73860cec
commit a3941517fc
1 changed files with 11 additions and 7 deletions
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18
kernel/rcu/Kconfig
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@ -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.
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 want to help to debug reduced OS jitter.
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