Hi Frederic,
On 9/7/2022 5:40 AM, Frederic Weisbecker wrote:
>>
>> diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
>> index bd8f39ee2cd0..e3344c262672 100644
>> --- a/kernel/rcu/tree_nocb.h
>> +++ b/kernel/rcu/tree_nocb.h
>> @@ -382,15 +382,19 @@ static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
>> unsigned long j, unsigned long flush_flags)
>> {
>> bool ret;
>> + bool was_alldone;
>>
>> if (!rcu_rdp_is_offloaded(rdp))
>> return true;
>> rcu_lockdep_assert_cblist_protected(rdp);
>> rcu_nocb_bypass_lock(rdp);
>> + if (flush_flags & FLUSH_BP_WAKE)
>> + was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
>> +
> You can check that outside bypass lock (but you still need nocb_lock).
Right, ok. I can make it outside the bypass lock, and the nocb_lock is implied
by rcu_lockdep_assert_cblist_protected().
>
>> ret = rcu_nocb_do_flush_bypass(rdp, rhp, j, flush_flags);
>>
>> - if (flush_flags & FLUSH_BP_WAKE)
>> - wake_nocb_gp(rdp, true);
>> + if (flush_flags & FLUSH_BP_WAKE && was_alldone)
>> + wake_nocb_gp(rdp, false);
> That doesn't check if the bypass list was empty.
thanks, will add your suggested optimization, however I have a general question:
For the case where the bypass list is empty, where does rcu_barrier() do a wake
up of the nocb GP thread after entrain()?
I don't see a call to __call_rcu_nocb_wake() like rcutree_migrate_callbacks()
does. Is the wake up done in some other path?
thanks,
- Joel
