On 2022/8/23 0:35, Paul E. McKenney wrote:
> 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.
How about I post v5 and just do this simplification? Patch 1/2 seems to require
further discussion and in-depth analysis, which may take a long time.
>
> 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
>>
> .
>
--
Regards,
Zhen Lei
