On Wed, Oct 12, 2016 at 11:12:51AM -0400, Luiz Capitulino wrote:
> Hi,
>
> We have the following patch applied to the RT tree:
>
> commit a9d3cc781a3306bfa332fa7cb6134b70696058d5
> Author: Josh Cartwright <joshc@xxxxxx>
> Date: Tue Oct 27 07:31:53 2015 -0500
>
> net: Make synchronize_rcu_expedited() conditional on !RT_FULL
>
> However, as noted by Michael, making rcu_normal=1 default in the
> RT kernel should have the same effect (ie. not calling
> synchronize_sched_expedited()).
>
> So, honest question, is there a reason not to:
>
> 1. Drop the patch above
> 2. Make rcu_normal=1 default?
I think this is probably a cleaner way to fix the problems which
motivated this patch in the first place. In my defense, the above patch
predates rcu_normal :).
Something like this, perhaps?
Julia
-- 8< --
Subject: [PATCH] rcu: enable rcu_normal_after_boot by default for RT
The forcing of an expedited grace period is an expensive and very
RT-application unfriendly operation, as it forcibly preempts all running
tasks on CPUs which are preventing the gp from expiring.
By default, as a policy decision, disable the expediting of grace
periods (after boot) on configurations which enable PREEMPT_RT_FULL.
Suggested-by: Luiz Capitulino <lcapitulino@xxxxxxxxxx>
Signed-off-by: Julia Cartwright <julia@xxxxxx>
---
kernel/rcu/update.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index b40d346..4975917 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -63,7 +63,7 @@ MODULE_ALIAS("rcupdate");
#ifndef CONFIG_TINY_RCU
module_param(rcu_expedited, int, 0);
module_param(rcu_normal, int, 0);
-static int rcu_normal_after_boot;
+static int rcu_normal_after_boot = IS_ENABLED(CONFIG_PREEMPT_RT_FULL);
module_param(rcu_normal_after_boot, int, 0);
#endif /* #ifndef CONFIG_TINY_RCU */
--
2.9.3
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