On 2022/9/1 19:11, Frederic Weisbecker wrote: > 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 OK, I got it. CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y takes effect only when there are no 'rcu_nocbs=' and 'nohz_full='. > > or > > NOCB CPUs = all > NOHZ_FULL CPUs = 7 > > The second makes more sense IMHO but that should be in a separate change. OK, in this case, CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y takes effect only when there is no 'rcu_nocbs='. > > Thanks. > . > -- Regards, Zhen Lei
