On Tue, Jun 21, 2022 at 10:41:54AM +0530, Neeraj Upadhyay wrote: > > > On 6/21/2022 3:47 AM, Paul E. McKenney wrote: > > 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> > > --- > > Reviewed-by: Neeraj Upadhyay <quic_neeraju@xxxxxxxxxxx> > > > 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 > > Minor : "caused by" ? Good catch, fixed, thank you! I applied your Reviewed-by to this series as well, and thank you for that as well. Thanx, Paul > Thanks > Neeraj > > > + 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
