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| author | Paul E. McKenney <paulmck@kernel.org> | 2021-11-24 15:12:15 -0800 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2021-12-09 10:52:11 -0800 |
| commit | ab97152f88a4d580b89f0b7cc3028ffac438216f (patch) | |
| tree | 8573b1e28c6fb1124da5421b8733325fac3bf8ea /Documentation/admin-guide | |
| parent | 3063b33a347c088e87516764d487e46fea3dfc94 (diff) | |
| download | lwn-ab97152f88a4d580b89f0b7cc3028ffac438216f.tar.gz lwn-ab97152f88a4d580b89f0b7cc3028ffac438216f.zip | |
rcu-tasks: Use more callback queues if contention encountered
The rcupdate.rcu_task_enqueue_lim module parameter allows system
administrators to tune the number of callback queues used by the RCU
Tasks flavors. However if callback storms are infrequent, it would
be better to operate with a single queue on a given system unless and
until that system actually needed more queues. Systems not needing
more queues can then avoid the overhead of checking the extra queues
and especially avoid the overhead of fanning workqueue handlers out to
all CPUs to invoke callbacks.
This commit therefore switches to using all the CPUs' callback queues if
call_rcu_tasks_generic() encounters too much lock contention. The amount
of lock contention to tolerate defaults to 100 contended lock acquisitions
per jiffy, and can be adjusted using the new rcupdate.rcu_task_contend_lim
module parameter.
Such switching is undertaken only if the rcupdate.rcu_task_enqueue_lim
module parameter is negative, which is its default value (-1).
This allows savvy systems administrators to set the number of queues
to some known good value and to not have to worry about the kernel doing
any second guessing.
[ paulmck: Apply feedback from Guillaume Tucker and kernelci. ]
Reported-by: Martin Lau <kafai@fb.com>
Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'Documentation/admin-guide')
| -rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 9b09fc5dfe66..089f4c5f8225 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4805,6 +4805,14 @@ period to instead use normal non-expedited grace-period processing. + rcupdate.rcu_task_contend_lim= [KNL] + Set the minimum number of callback-queuing-time + lock-contention events per jiffy required to + cause the RCU Tasks flavors to switch to per-CPU + callback queuing. This switching only occurs + when rcupdate.rcu_task_enqueue_lim is set to + the default value of -1. + rcupdate.rcu_task_enqueue_lim= [KNL] Set the number of callback queues to use for the RCU Tasks family of RCU flavors. The default |