On Wed, Aug 17, 2022 at 09:42:53AM +0800, Zhen Lei wrote:
> When CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y or CONFIG_NO_HZ_FULL=y, additional
> CPUs need to be added to 'rcu_nocb_mask'. But 'rcu_nocb_mask' may be not
> available now, due to 'rcu_nocbs' is not specified. Check and initialize
> 'rcu_nocb_mask' before using it. This code simplification strictly follows
> this logic, compared with old implementations, unnecessary crossovers are
> avoided and easy to understand.
>
> Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
This looks like a nice simplification, but I will wait for your response
on Patch 1/1 before trying it out.
Thanx, Paul
> ---
> kernel/rcu/tree_nocb.h | 32 +++++++++-----------------------
> 1 file changed, 9 insertions(+), 23 deletions(-)
>
> diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
> index ff763e7dc53551f..3c59b12f4465af1 100644
> --- a/kernel/rcu/tree_nocb.h
> +++ b/kernel/rcu/tree_nocb.h
> @@ -1209,44 +1209,30 @@ 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;
> + const struct cpumask *cpumask = NULL;
>
> #if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
> - if (!cpumask_available(rcu_nocb_mask)) {
> - need_rcu_nocb_mask = true;
> - offload_all = true;
> - }
> -#endif /* #if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) */
> -
> -#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) */
> + cpumask = cpu_possible_mask;
> +#elif defined(CONFIG_NO_HZ_FULL)
> + if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
> + cpumask = tick_nohz_full_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);
> }
>
> if (!cpumask_available(rcu_nocb_mask))
> 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,
> --
> 2.25.1
>
