On 2022/5/13 23:05, Paul E. McKenney wrote:
> On Tue, Apr 26, 2022 at 03:36:26PM +0800, Zhen Lei wrote:
>> The local variable 'need_rcu_nocb_mask' is true only if CONFIG_NO_HZ_FULL
>> is defined. So branch "if (need_rcu_nocb_mask)" can be moved within the
>> scope of "#if defined(CONFIG_NO_HZ_FULL)". At this point, using variable
>> 'need_rcu_nocb_mask' is not necessary, so delete it.
>>
>> No functional changes, but the code looks a little more concise.
>>
>> Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
>
> First, please accept my apologies for the late reply and for the
> overly active spam filters.
>
> One question below.
>
> Thanx, Paul
>
>> ---
>> kernel/rcu/tree_nocb.h | 8 ++------
>> 1 file changed, 2 insertions(+), 6 deletions(-)
>>
>> diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
>> index 636d0546a4e932e..1e334e217f0afb7 100644
>> --- a/kernel/rcu/tree_nocb.h
>> +++ b/kernel/rcu/tree_nocb.h
>> @@ -1165,15 +1165,10 @@ EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload);
>> void __init rcu_init_nohz(void)
>> {
>> int cpu;
>> - bool need_rcu_nocb_mask = false;
>> struct rcu_data *rdp;
>>
>> #if defined(CONFIG_NO_HZ_FULL)
>> - if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
>> - need_rcu_nocb_mask = true;
>> -#endif /* #if defined(CONFIG_NO_HZ_FULL) */
>> -
>> - if (need_rcu_nocb_mask) {
>
> Could you please test this on a kernel built with CONFIG_NO_HZ_FULL=n
> and CONFIG_RCU_NOCB_CPU=y? If that works, please add an explanation
OK, I will test it.
> of why it works to the commit log above and repost the patch.
Sorry, If I had written pseudocode in the commit log, it would have been clear, as below:
-----------------before-----------------
bool need_rcu_nocb_mask = false;
#if defined(CONFIG_NO_HZ_FULL)
if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
need_rcu_nocb_mask = true; <---- //Move it here, then delete all 'need_rcu_nocb_mask' related code
#endif /* #if defined(CONFIG_NO_HZ_FULL) */ |
|
if (need_rcu_nocb_mask) { | //Can only be true above
... -----
}
-----------------after-----------------
#if defined(CONFIG_NO_HZ_FULL)
if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask)) {
...
}
#endif /* #if defined(CONFIG_NO_HZ_FULL) */
I'm doing clean up on the premise that the original code is correct.
>
>> + if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask)) {
>> 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");
>> @@ -1182,6 +1177,7 @@ void __init rcu_init_nohz(void)
>> }
>> rcu_nocb_is_setup = true;
>> }
>> +#endif /* #if defined(CONFIG_NO_HZ_FULL) */
>>
>> if (!rcu_nocb_is_setup)
>> return;
>> --
>> 2.26.0.106.g9fadedd
>>
> .
>
--
Regards,
Zhen Lei
