linux-kernel - [PATCH 2/2] locking/lockdep: Make global debug

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Date:   Thu, 18 Oct 2018 21:45:18 -0400
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Waiman Long <longman@...hat.com>
Subject: [PATCH 2/2] locking/lockdep: Make global debug_locks* variables read-mostly

Make the frequently used lockdep global variable debug_locks read-mostly.
As debug_locks_silent is sometime used together with debug_locks,
it is also made read-mostly so that they can be close together.

With false cacheline sharing, cacheline contention problem can happen
depending on what get put into the same cacheline as debug_locks.

Signed-off-by: Waiman Long <longman@...hat.com>
---
 include/linux/debug_locks.h | 4 ++--
 lib/debug_locks.c           | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/debug_locks.h b/include/linux/debug_locks.h
index 120225e..257ab3c 100644
--- a/include/linux/debug_locks.h
+++ b/include/linux/debug_locks.h
@@ -8,8 +8,8 @@
 
 struct task_struct;
 
-extern int debug_locks;
-extern int debug_locks_silent;
+extern int debug_locks __read_mostly;
+extern int debug_locks_silent __read_mostly;
 
 
 static inline int __debug_locks_off(void)
diff --git a/lib/debug_locks.c b/lib/debug_locks.c
index 124fdf2..ce51749 100644
--- a/lib/debug_locks.c
+++ b/lib/debug_locks.c
@@ -21,7 +21,7 @@
  * that would just muddy the log. So we report the first one and
  * shut up after that.
  */
-int debug_locks = 1;
+int debug_locks __read_mostly = 1;
 EXPORT_SYMBOL_GPL(debug_locks);
 
 /*
@@ -29,7 +29,7 @@
  * 'silent failure': nothing is printed to the console when
  * a locking bug is detected.
  */
-int debug_locks_silent;
+int debug_locks_silent __read_mostly;
 EXPORT_SYMBOL_GPL(debug_locks_silent);
 
 /*
-- 
1.8.3.1