linux-kernel - Re: [PATCH v4 04/16] locking/rwsem: Implement a new locking scheme

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Date:   Tue, 16 Apr 2019 15:22:18 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Davidlohr Bueso <dave@...olabs.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        huang ying <huang.ying.caritas@...il.com>
Subject: Re: [PATCH v4 04/16] locking/rwsem: Implement a new locking scheme

On Sat, Apr 13, 2019 at 01:22:47PM -0400, Waiman Long wrote:
> +#define RWSEM_COUNT_LOCKED(c)	((c) & RWSEM_LOCK_MASK)

The above doesn't seem to make it more readable or shorter.

--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -192,7 +192,7 @@ static inline bool rwsem_try_write_lock(
 {
 	long new;
 
-	if (RWSEM_COUNT_LOCKED(count))
+	if (count & RWSEM_LOCK_MASK)
 		return false;
 
 	new = count + RWSEM_WRITER_LOCKED -
@@ -214,7 +214,7 @@ static inline bool rwsem_try_write_lock_
 {
 	long count = atomic_long_read(&sem->count);
 
-	while (!RWSEM_COUNT_LOCKED(count)) {
+	while (!(count & RWSEM_LOCK_MASK)) {
 		if (atomic_long_try_cmpxchg_acquire(&sem->count, &count,
 					count + RWSEM_WRITER_LOCKED)) {
 			rwsem_set_owner(sem);
@@ -393,7 +393,7 @@ __rwsem_down_read_failed_common(struct r
 	 * If there are no writers and we are first in the queue,
 	 * wake our own waiter to join the existing active readers !
 	 */
-	if (!RWSEM_COUNT_LOCKED(count) ||
+	if (!(count & RWSEM_LOCK_MASK) ||
 	   (!(count & RWSEM_WRITER_MASK) && (adjustment & RWSEM_FLAG_WAITERS)))
 		__rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
 
@@ -522,7 +522,7 @@ __rwsem_down_write_failed_common(struct
 			lockevent_inc(rwsem_sleep_writer);
 			set_current_state(state);
 			count = atomic_long_read(&sem->count);
-		} while (RWSEM_COUNT_LOCKED(count));
+		} while (count & RWSEM_LOCK_MASK);
 
 		raw_spin_lock_irq(&sem->wait_lock);
 	}