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From f707470b0622333c42926ac322c72c3f1786d20b Mon Sep 17 00:00:00 2001 |
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From: Waiman Long <longman@redhat.com> |
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Date: Thu, 18 Oct 2018 21:45:17 -0400 |
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Subject: [PATCH 004/145] locking/lockdep: Fix debug_locks off performance |
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problem |
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|
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[ Upstream commit 9506a7425b094d2f1d9c877ed5a78f416669269b ] |
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|
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It was found that when debug_locks was turned off because of a problem |
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found by the lockdep code, the system performance could drop quite |
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significantly when the lock_stat code was also configured into the |
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kernel. For instance, parallel kernel build time on a 4-socket x86-64 |
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server nearly doubled. |
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|
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Further analysis into the cause of the slowdown traced back to the |
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frequent call to debug_locks_off() from the __lock_acquired() function |
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probably due to some inconsistent lockdep states with debug_locks |
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off. The debug_locks_off() function did an unconditional atomic xchg |
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to write a 0 value into debug_locks which had already been set to 0. |
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This led to severe cacheline contention in the cacheline that held |
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debug_locks. As debug_locks is being referenced in quite a few different |
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places in the kernel, this greatly slow down the system performance. |
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|
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To prevent that trashing of debug_locks cacheline, lock_acquired() |
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and lock_contended() now checks the state of debug_locks before |
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proceeding. The debug_locks_off() function is also modified to check |
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debug_locks before calling __debug_locks_off(). |
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|
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Signed-off-by: Waiman Long <longman@redhat.com> |
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Cc: Andrew Morton <akpm@linux-foundation.org> |
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Cc: Linus Torvalds <torvalds@linux-foundation.org> |
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Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> |
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Cc: Peter Zijlstra <peterz@infradead.org> |
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Cc: Thomas Gleixner <tglx@linutronix.de> |
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Cc: Will Deacon <will.deacon@arm.com> |
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Link: http://lkml.kernel.org/r/1539913518-15598-1-git-send-email-longman@redhat.com |
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Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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Signed-off-by: Sasha Levin <sashal@kernel.org> |
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--- |
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kernel/locking/lockdep.c | 4 ++-- |
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lib/debug_locks.c | 2 +- |
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2 files changed, 3 insertions(+), 3 deletions(-) |
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|
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diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c |
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index dd13f865ad40..26b57e24476f 100644 |
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--- a/kernel/locking/lockdep.c |
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+++ b/kernel/locking/lockdep.c |
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@@ -4122,7 +4122,7 @@ void lock_contended(struct lockdep_map *lock, unsigned long ip) |
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{ |
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unsigned long flags; |
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|
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- if (unlikely(!lock_stat)) |
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+ if (unlikely(!lock_stat || !debug_locks)) |
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return; |
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|
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if (unlikely(current->lockdep_recursion)) |
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@@ -4142,7 +4142,7 @@ void lock_acquired(struct lockdep_map *lock, unsigned long ip) |
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{ |
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unsigned long flags; |
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|
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- if (unlikely(!lock_stat)) |
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+ if (unlikely(!lock_stat || !debug_locks)) |
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return; |
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|
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if (unlikely(current->lockdep_recursion)) |
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diff --git a/lib/debug_locks.c b/lib/debug_locks.c |
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index 96c4c633d95e..124fdf238b3d 100644 |
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--- a/lib/debug_locks.c |
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+++ b/lib/debug_locks.c |
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@@ -37,7 +37,7 @@ EXPORT_SYMBOL_GPL(debug_locks_silent); |
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*/ |
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int debug_locks_off(void) |
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{ |
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- if (__debug_locks_off()) { |
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+ if (debug_locks && __debug_locks_off()) { |
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if (!debug_locks_silent) { |
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console_verbose(); |
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return 1; |
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-- |
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2.19.1 |
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