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ef42ef8451
[ Upstream commit 9506a7425b ]
It was found that when debug_locks was turned off because of a problem
found by the lockdep code, the system performance could drop quite
significantly when the lock_stat code was also configured into the
kernel. For instance, parallel kernel build time on a 4-socket x86-64
server nearly doubled.
Further analysis into the cause of the slowdown traced back to the
frequent call to debug_locks_off() from the __lock_acquired() function
probably due to some inconsistent lockdep states with debug_locks
off. The debug_locks_off() function did an unconditional atomic xchg
to write a 0 value into debug_locks which had already been set to 0.
This led to severe cacheline contention in the cacheline that held
debug_locks. As debug_locks is being referenced in quite a few different
places in the kernel, this greatly slow down the system performance.
To prevent that trashing of debug_locks cacheline, lock_acquired()
and lock_contended() now checks the state of debug_locks before
proceeding. The debug_locks_off() function is also modified to check
debug_locks before calling __debug_locks_off().
Signed-off-by: Waiman Long <longman@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/1539913518-15598-1-git-send-email-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
49 lines
1.2 KiB
C
49 lines
1.2 KiB
C
/*
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* lib/debug_locks.c
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*
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* Generic place for common debugging facilities for various locks:
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* spinlocks, rwlocks, mutexes and rwsems.
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*
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* Started by Ingo Molnar:
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*
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* Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
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*/
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#include <linux/rwsem.h>
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#include <linux/mutex.h>
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#include <linux/export.h>
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#include <linux/spinlock.h>
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#include <linux/debug_locks.h>
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/*
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* We want to turn all lock-debugging facilities on/off at once,
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* via a global flag. The reason is that once a single bug has been
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* detected and reported, there might be cascade of followup bugs
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* that would just muddy the log. So we report the first one and
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* shut up after that.
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*/
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int debug_locks = 1;
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EXPORT_SYMBOL_GPL(debug_locks);
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/*
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* The locking-testsuite uses <debug_locks_silent> to get a
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* 'silent failure': nothing is printed to the console when
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* a locking bug is detected.
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*/
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int debug_locks_silent;
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EXPORT_SYMBOL_GPL(debug_locks_silent);
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/*
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* Generic 'turn off all lock debugging' function:
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*/
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int debug_locks_off(void)
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{
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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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}
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return 0;
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}
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EXPORT_SYMBOL_GPL(debug_locks_off);
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