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@xxxxxxxxxx> Reported-by: Uladzislau Rezki <urezki@xxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> --- 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
