Re: [PATCH 14/16] rcu: Remove redundant checks for rcu_scheduler_fully_active

Paul E. McKenney
2014-07-23T12:27:59Z

On Wed, Jul 23, 2014 at 01:09:51AM -0400, Pranith Kumar wrote:
> rcu_scheduler_fully_active is set to true early in the boot process.
>
> The check for this flag is only needed in rcu_prepare_kthreads() as this
> function is called before the above flag is set. All other checks are redundant.
> Hence this commit removes those redundant checks.
>
> Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>

This might actually work, but the checks are cheap, don't happen very often,
and make it much easier to modify the code. So sorry, but no.

Thanx, Paul

> ---
> kernel/rcu/tree_plugin.h | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 9a50e1d..541c776 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -1341,7 +1341,7 @@ static void rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
> if (&rcu_preempt_state != rsp)
> return 0;
>
> - if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0)
> + if (rnp->qsmaskinit == 0)
> return 0;
>
> rsp->boost = 1;
> @@ -1486,9 +1486,10 @@ static void rcu_prepare_kthreads(int cpu)
> struct rcu_node *rnp = rdp->mynode;
>
> /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
> - if (rcu_scheduler_fully_active)
> - rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
> + if (!rcu_scheduler_fully_active)
> + return;
>
> + rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
> rcu_spawn_all_nocb_kthreads(cpu);
> }
>
> @@ -2508,9 +2509,8 @@ static void rcu_spawn_all_nocb_kthreads(int cpu)
> {
> struct rcu_state *rsp;
>
> - if (rcu_scheduler_fully_active)
> - for_each_rcu_flavor(rsp)
> - rcu_spawn_one_nocb_kthread(rsp, cpu);
> + for_each_rcu_flavor(rsp)
> + rcu_spawn_one_nocb_kthread(rsp, cpu);
> }
>
> /*
> --
> 2.0.0.rc2
>