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| author | Paul E. McKenney <paulmck@kernel.org> | 2024-10-09 11:00:39 -0700 |
|---|---|---|
| committer | Frederic Weisbecker <frederic@kernel.org> | 2024-11-12 21:41:08 +0100 |
| commit | f30e2582a79173e6b6f8ebb44783085b6ec78de1 (patch) | |
| tree | 34481e9a749f970eaa66abb4d0c5d9ce855ff836 /kernel/rcu | |
| parent | 5d2501f42cf8caad1abb44a37f20195a52e1cf07 (diff) | |
| download | linux-f30e2582a79173e6b6f8ebb44783085b6ec78de1.tar.gz linux-f30e2582a79173e6b6f8ebb44783085b6ec78de1.tar.bz2 linux-f30e2582a79173e6b6f8ebb44783085b6ec78de1.zip | |
rcu: Add rcuog kthreads to RCU_NOCB_CPU help text
The RCU_NOCB_CPU help text currently fails to mention rcuog kthreads,
so this commit adds this information.
Reported-by: Olivier Langlois <olivier@trillion01.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/Kconfig | 28 |
1 files changed, 18 insertions, 10 deletions
diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig index 3e079de0f5b4..b9b6bc55185d 100644 --- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -249,16 +249,24 @@ config RCU_NOCB_CPU 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 "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. + 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 "x" is "p" for RCU-preempt (PREEMPTION kernels) + and "s" for RCU-sched (!PREEMPTION kernels). This option + also creates another kthread for each sqrt(nr_cpu_ids) CPUs + ("rcuog/N", where N is the first CPU in that group to come + online), which handles grace periods for its group. Nothing + prevents these kthreads 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 sqrt(nr_cpu_ids) grouping may be overridden using the + rcutree.rcu_nocb_gp_stride kernel boot parameter. This can + be especially helpful for smaller numbers of CPUs, where + sqrt(nr_cpu_ids) can be a bit of a blunt instrument. Say Y here if you need reduced OS jitter, despite added overhead. Say N here if you are unsure. |