Messages in this thread Patch in this message | | | From | "Paul E. McKenney" <> | Subject | [PATCH rcu 3/3] doc: Document rcutree.nocb_nobypass_lim_per_jiffy kernel parameter | Date | Mon, 20 Jun 2022 15:17:57 -0700 |
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This commit provides documentation for the kernel parameter controlling RCU's handling of callback floods on offloaded (rcu_nocbs) CPUs. This parameter might be obscure, but it is always there when you need it.
Reported-by: Frederic Weisbecker <frederic@kernel.org> Reported-by: Uladzislau Rezki <urezki@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> --- Documentation/admin-guide/kernel-parameters.txt | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index bdf431bdbfdc4..a30890141b1a5 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4681,6 +4681,19 @@ invoked in the context of an rcuoc kthread, which scheduler will preempt as it does any other task. + rcutree.nocb_nobypass_lim_per_jiffy= [KNL] + On callback-offloaded (rcu_nocbs) CPUs, + RCU reduces the lock contention that would + otherwise be caused callback floods through + use of the ->nocb_bypass list. However, in the + common non-flooded case, RCU queues directly to + the main ->cblist in order to avoid the extra + overhead of the ->nocb_bypass list and its lock. + But if there are too many callbacks queued during + a single jiffy, RCU pre-queues the callbacks into + the ->nocb_bypass queue. The definition of "too + many" is supplied by this kernel boot parameter. + rcutree.rcu_nocb_gp_stride= [KNL] Set the number of NOCB callback kthreads in each group, which defaults to the square root -- 2.31.1.189.g2e36527f23
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