On Thu, Sep 01, 2022 at 03:25:20AM -0700, Paul E. McKenney wrote: > On Thu, Sep 01, 2022 at 11:15:57AM +0200, Frederic Weisbecker wrote: > > > +#elif defined(CONFIG_NO_HZ_FULL) > > > + if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask)) > > > + cpumask = tick_nohz_full_mask; > > > +#endif > > > > A subtle behaviour difference here too: CONFIG_RCU_NOCB_CPU_DEFAULT_ALL will > > now override nohz_full= > > > > I don't mind, it's probably what we want in the end, but the changelog should > > tell about it, or even better, this should be a separate change. > > Good point. Perhaps the key point is that if there is nohz_full=, > rcu_nocbs=, and CONFIG_RCU_NOCB_CPU_DEFAULT_ALL, we still need rcu_nocbs= > to include at least those bits set by nohz_full=. Not sure I get what you mean. nohz_full= should in any case always force rcu_nocbs at least on the nohz_full CPUs. For example assuming the following combination: rcu_nocbs=6, nohz_full=7 AND CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y, then the result should be: NOCB CPUs = 6,7 NOHZ_FULL CPUs = 7 (CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y is overriden by rcu_nocbs=6). Now if we have nohz_full=7 AND CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y, then the result is expected to be either: NOCB CPUs = 7 (upstream behaviour) NOHZ_FULL CPUs = 7 or NOCB CPUs = all NOHZ_FULL CPUs = 7 The second makes more sense IMHO but that should be in a separate change. Thanks.
