Messages in this thread Patch in this message |  | | From | guoren@kernel ... | Subject | [PATCH] locking/qspinlock: Optimize pending state waiting for unlock | Date | Sat, 24 Dec 2022 07:05:45 -0500 |
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From: Guo Ren <guoren@linux.alibaba.com>
When we're pending, we only care about lock value. The xchg_tail wouldn't affect the pending state. That means the hardware thread could stay in a sleep state and leaves the rest execution units' resources of pipeline to other hardware threads. This optimization may work only for SMT scenarios because the granularity between cores is cache-block.
Signed-off-by: Guo Ren <guoren@linux.alibaba.com> Signed-off-by: Guo Ren <guoren@kernel.org> Cc: Waiman Long <longman@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Will Deacon <will@kernel.org> Cc: Ingo Molnar <mingo@redhat.com> --- kernel/locking/qspinlock.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 2b23378775fe..ebe6b8ec7cb3 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -371,7 +371,7 @@ void __lockfunc queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) /* * We're pending, wait for the owner to go away. * - * 0,1,1 -> 0,1,0 + * 0,1,1 -> *,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 @@ -380,7 +380,7 @@ void __lockfunc queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) * barriers. */ if (val & _Q_LOCKED_MASK) - atomic_cond_read_acquire(&lock->val, !(VAL & _Q_LOCKED_MASK)); + smp_cond_load_acquire(&lock->locked, !VAL); /* * take ownership and clear the pending bit. -- 2.36.1
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