On Thu, Sep 01, 2022 at 09:25:06PM +0800, Leizhen (ThunderTown) wrote:
>
>
> On 2022/9/1 21:14, Zhen Lei wrote:
> > In kernels built with either CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y or
> > CONFIG_NO_HZ_FULL=y, additional CPUs must be added to rcu_nocb_mask.
> > Except that kernels booted without the rcu_nocbs= will not have
> > allocated rcu_nocb_mask. And the current rcu_init_nohz() function uses
> > its need_rcu_nocb_mask and offload_all local variables to track the
> > rcu_nocb and nohz_full state.
> >
> > But there is a much simpler approach, namely creating a cpumask pointer
> > to track the default and then using cpumask_available() to check the
> > rcu_nocb_mask state. This commit takes this approach, thereby simplifying
> > and shortening the rcu_init_nohz() function.
> >
> > Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
>
> Sorry, I forgot remove this "Signed-off-by".
Not a problem, especially given that in view of my oversight on the
previous version, I am going to let Frederic take first crack at this
version. ;-)
Thanx, Paul
> > Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> > ---
> > kernel/rcu/tree_nocb.h | 35 ++++++++++++-----------------------
> > 1 file changed, 12 insertions(+), 23 deletions(-)
> >
> > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
> > index 0a5f0ef41484518..8b6dceeabde0b4d 100644
> > --- a/kernel/rcu/tree_nocb.h
> > +++ b/kernel/rcu/tree_nocb.h
> > @@ -1210,45 +1210,34 @@ EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload);
> > void __init rcu_init_nohz(void)
> > {
> > int cpu;
> > - bool need_rcu_nocb_mask = false;
> > - bool offload_all = false;
> > struct rcu_data *rdp;
> > -
> > -#if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
> > - if (!rcu_state.nocb_is_setup) {
> > - need_rcu_nocb_mask = true;
> > - offload_all = true;
> > - }
> > -#endif /* #if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) */
> > + const struct cpumask *cpumask = NULL;
> >
> > #if defined(CONFIG_NO_HZ_FULL)
> > - if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask)) {
> > - need_rcu_nocb_mask = true;
> > - offload_all = false; /* NO_HZ_FULL has its own mask. */
> > - }
> > -#endif /* #if defined(CONFIG_NO_HZ_FULL) */
> > + if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
> > + cpumask = tick_nohz_full_mask;
> > +#endif
> > +
> > +#if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
> > + if (!rcu_state.nocb_is_setup && !cpumask)
> > + cpumask = cpu_possible_mask;
> > +#endif
> >
> > - if (need_rcu_nocb_mask) {
> > + if (cpumask) {
> > if (!cpumask_available(rcu_nocb_mask)) {
> > if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
> > pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
> > return;
> > }
> > }
> > +
> > + cpumask_or(rcu_nocb_mask, rcu_nocb_mask, cpumask);
> > rcu_state.nocb_is_setup = true;
> > }
> >
> > if (!rcu_state.nocb_is_setup)
> > return;
> >
> > -#if defined(CONFIG_NO_HZ_FULL)
> > - if (tick_nohz_full_running)
> > - cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
> > -#endif /* #if defined(CONFIG_NO_HZ_FULL) */
> > -
> > - if (offload_all)
> > - cpumask_setall(rcu_nocb_mask);
> > -
> > if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
> > pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
> > cpumask_and(rcu_nocb_mask, cpu_possible_mask,
> >
>
> --
> Regards,
> Zhen Lei
