Commit-ID: 53bf57fab7321fb42b703056a4c80fc9d986d170 Gitweb: https://git.kernel.org/tip/53bf57fab7321fb42b703056a4c80fc9d986d170 Author: Peter Zijlstra <pet...@infradead.org> AuthorDate: Wed, 26 Sep 2018 13:01:18 +0200 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Tue, 16 Oct 2018 17:33:53 +0200
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) <pet...@infradead.org> Acked-by: Will Deacon <will.dea...@arm.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Cc: andrea.pa...@amarulasolutions.com Cc: long...@redhat.com Link: https://lkml.kernel.org/r/20181003130257.156322...@infradead.org Signed-off-by: Ingo Molnar <mi...@kernel.org> --- kernel/locking/qspinlock.c | 56 ++++++++++++++++++++++------------------------ 1 file 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
