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authorPaul E. McKenney <paulmck@kernel.org>2021-11-25 02:12:15 +0300
committerPaul E. McKenney <paulmck@kernel.org>2021-12-09 21:52:11 +0300
commitab97152f88a4d580b89f0b7cc3028ffac438216f (patch)
tree8573b1e28c6fb1124da5421b8733325fac3bf8ea /Documentation/admin-guide/kernel-parameters.txt
parent3063b33a347c088e87516764d487e46fea3dfc94 (diff)
downloadlinux-ab97152f88a4d580b89f0b7cc3028ffac438216f.tar.xz
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/kernel-parameters.txt')
-rw-r--r--Documentation/admin-guide/kernel-parameters.txt8
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