linux-kernel - Re: [patch] timer: Fix timers_update_migration(), and call it in tmigr

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Message-Id: <20170429214544.GK3956@linux.vnet.ibm.com>
Date:   Sat, 29 Apr 2017 14:45:44 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Mike Galbraith <efault@....de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>, Ingo Molnar <mingo@...e.hu>,
        Thomas Gleixner <tglx@...utronix.de>,
        PeterZijlstra <peterz@...radead.org>,
        Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [patch] timer: Fix timers_update_migration(), and call it in
 tmigr_init()

On Sat, Apr 29, 2017 at 08:20:33PM +0200, Mike Galbraith wrote:
> On Sat, 2017-04-29 at 11:06 -0700, Paul E. McKenney wrote:
> 
> > If someone will either repost a fresh series or point me at exactly
> > the set of patches to use, I will run it through rcutorture again.
> 
> Patchlet is against x86-tip/master.today.

So today's (as in Saturday April 29) x86-tip/master with the following
patch applied?

							Thanx, Paul

------------------------------------------------------------------------

timers_update_migration() is called by tick_nohz_activate() before
the late initcall tmigr_init() sets tmigr_enabled to true, resulting
in it updating neither timer_base.nohz_active nor .migration_enabled,
meaning we'll not kick an idling cpu in add_timer_on().

Remove redundant loop avoidance such that tick_nohz_activate() updates
timer_bases[].nohz_active as intended, and call it in tmigr_init() to
update timer_bases[].migration_enabled.

Signed-off-by: Mike Galbraith <efault@....de>
Fixes: ec2206b91d43 timer: Implement the hierarchical pull model
---
 kernel/time/timer.c           |    4 ----
 kernel/time/timer_migration.c |    1 +
 2 files changed, 1 insertion(+), 4 deletions(-)

--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -224,10 +224,6 @@ void timers_update_migration(bool update
 	bool on = sysctl_timer_migration && tick_nohz_active && tmigr_enabled;
 	unsigned int cpu;

-	/* Avoid the loop, if nothing to update */
-	if (this_cpu_read(timer_bases[BASE_GLOBAL].migration_enabled) == on)
-		return;
-
 	for_each_possible_cpu(cpu) {
 		per_cpu(timer_bases[BASE_LOCAL].migration_enabled, cpu) = on;
 		per_cpu(timer_bases[BASE_GLOBAL].migration_enabled, cpu) = on;
--- a/kernel/time/timer_migration.c
+++ b/kernel/time/timer_migration.c
@@ -649,6 +649,7 @@ static int __init tmigr_init(void)
 		goto hp_err;

 	tmigr_enabled = true;
+	timers_update_migration(false);
 	pr_info("Timer migration: %d hierarchy levels\n", tmigr_hierarchy_levels);
 	return 0;