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@xxxxxxxxx> 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? Thanx, Paul ------------------------------------------------------------------------ commit d9eaddf545fe8e3e2725e2fa0bf87b59b5667c14 Author: Wei Yang <richard.weiyang@xxxxxxxxx> 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@xxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> 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);