Messages in this thread | | | Date | Tue, 21 Jun 2022 10:41:54 +0530 | Subject | Re: [PATCH rcu 3/3] doc: Document rcutree.nocb_nobypass_lim_per_jiffy kernel parameter | From | Neeraj Upadhyay <> |
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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@kernel.org> > Reported-by: Uladzislau Rezki <urezki@gmail.com> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org> > ---
Reviewed-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
> 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" ?
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
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