Re: [PATCH] rcu: init and destroy rcu_synchronize when necessary

[Wei Yang <richard.weiyang@gmail.com>]

On Wed, Apr 15, 2020 at 05:24:00PM -0700, Paul E. McKenney wrote:
>On Wed, Apr 15, 2020 at 10:26:55PM +0000, Wei Yang wrote:
>> We would skip the rcu_synchronize if it is a duplicate call back function.
>> 
>> This is not necessary to init and destroy for them.
>> 
>> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>
>Applied, thank you!
>
>I edited the commit log a bit.  Could you please check below to make
>sure that I didn't mess anything up?
>

Yep, the changelog looks good to me :-)

Glad you like it.

>							Thanx, Paul
>
>------------------------------------------------------------------------
>
>commit d9eaddf545fe8e3e2725e2fa0bf87b59b5667c14
>Author: Wei Yang <richard.weiyang@gmail.com>
>Date:   Wed Apr 15 22:26:55 2020 +0000
>
>    rcu: Initialize and destroy rcu_synchronize only when necessary
>    
>    The __wait_rcu_gp() function unconditionally initializes and cleans up
>    each element of rs_array[], whether used or not.  This is slightly
>    wasteful and rather confusing, so this commit skips both initialization
>    and cleanup for duplicate callback functions.
>    
>    Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
>
>diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
>index 3ce63a9..351c322 100644
>--- a/kernel/rcu/update.c
>+++ b/kernel/rcu/update.c
>@@ -391,13 +391,14 @@ void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
> 			might_sleep();
> 			continue;
> 		}
>-		init_rcu_head_on_stack(&rs_array[i].head);
>-		init_completion(&rs_array[i].completion);
> 		for (j = 0; j < i; j++)
> 			if (crcu_array[j] == crcu_array[i])
> 				break;
>-		if (j == i)
>+		if (j == i) {
>+			init_rcu_head_on_stack(&rs_array[i].head);
>+			init_completion(&rs_array[i].completion);
> 			(crcu_array[i])(&rs_array[i].head, wakeme_after_rcu);
>+		}
> 	}
> 
> 	/* Wait for all callbacks to be invoked. */
>@@ -408,9 +409,10 @@ void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
> 		for (j = 0; j < i; j++)
> 			if (crcu_array[j] == crcu_array[i])
> 				break;
>-		if (j == i)
>+		if (j == i) {
> 			wait_for_completion(&rs_array[i].completion);
>-		destroy_rcu_head_on_stack(&rs_array[i].head);
>+			destroy_rcu_head_on_stack(&rs_array[i].head);
>+		}
> 	}
> }
> EXPORT_SYMBOL_GPL(__wait_rcu_gp);

-- 
Wei Yang
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