diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2018-09-26 14:01:18 +0300 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2018-10-16 18:33:53 +0300 |
| commit | 53bf57fab7321fb42b703056a4c80fc9d986d170 (patch) | |
| tree | 9235fe433960327c1da49e63e796e992b196173f /kernel/locking/qspinlock.c | |
| parent | ec57e2f0acb01710cd465bc04495ed03a9e0fea1 (diff) | |
| download | linux-53bf57fab7321fb42b703056a4c80fc9d986d170.tar.xz | |
locking/qspinlock: Re-order code
Flip the branch condition after atomic_fetch_or_acquire(_Q_PENDING_VAL)
such that we loose the indent. This also result in a more natural code
flow IMO.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: andrea.parri@amarulasolutions.com
Cc: longman@redhat.com
Link: https://lkml.kernel.org/r/20181003130257.156322446@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/locking/qspinlock.c')
| -rw-r--r-- | kernel/locking/qspinlock.c | 56 |
1 files changed, 27 insertions, 29 deletions
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index bfaeb05123ff..ec343276f975 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -330,39 +330,37 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) * 0,0,1 -> 0,1,1 ; pending */ val = atomic_fetch_or_acquire(_Q_PENDING_VAL, &lock->val); - if (!(val & ~_Q_LOCKED_MASK)) { - /* - * We're pending, wait for the owner to go away. - * - * *,1,1 -> *,1,0 - * - * this wait loop must be a load-acquire such that we match the - * store-release that clears the locked bit and create lock - * sequentiality; this is because not all - * clear_pending_set_locked() implementations imply full - * barriers. - */ - if (val & _Q_LOCKED_MASK) { - atomic_cond_read_acquire(&lock->val, - !(VAL & _Q_LOCKED_MASK)); - } - - /* - * take ownership and clear the pending bit. - * - * *,1,0 -> *,0,1 - */ - clear_pending_set_locked(lock); - qstat_inc(qstat_lock_pending, true); - return; + /* + * If we observe any contention; undo and queue. + */ + if (unlikely(val & ~_Q_LOCKED_MASK)) { + if (!(val & _Q_PENDING_MASK)) + clear_pending(lock); + goto queue; } /* - * If pending was clear but there are waiters in the queue, then - * we need to undo our setting of pending before we queue ourselves. + * We're pending, wait for the owner to go away. + * + * 0,1,1 -> 0,1,0 + * + * this wait loop must be a load-acquire such that we match the + * store-release that clears the locked bit and create lock + * sequentiality; this is because not all + * clear_pending_set_locked() implementations imply full + * barriers. + */ + if (val & _Q_LOCKED_MASK) + atomic_cond_read_acquire(&lock->val, !(VAL & _Q_LOCKED_MASK)); + + /* + * take ownership and clear the pending bit. + * + * 0,1,0 -> 0,0,1 */ - if (!(val & _Q_PENDING_MASK)) - clear_pending(lock); + clear_pending_set_locked(lock); + qstat_inc(qstat_lock_pending, true); + return; /* * End of pending bit optimistic spinning and beginning of MCS |