linux-kernel - [PATCH v6 4/9] csky: locks: Optimize coding convention

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Message-Id: <1617201040-83905-5-git-send-email-guoren@kernel.org>
Date:   Wed, 31 Mar 2021 14:30:35 +0000
From:   guoren@...nel.org
To:     guoren@...nel.org
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-csky@...r.kernel.org, linux-arch@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-xtensa@...ux-xtensa.org,
        openrisc@...ts.librecores.org, sparclinux@...r.kernel.org,
        Guo Ren <guoren@...ux.alibaba.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: [PATCH v6 4/9] csky: locks: Optimize coding convention

From: Guo Ren <guoren@...ux.alibaba.com>

 - Using smp_cond_load_acquire in arch_spin_lock by Peter's
   advice.
 - Using __smp_acquire_fence in arch_spin_trylock
 - Using smp_store_release in arch_spin_unlock

All above are just coding conventions and won't affect the
function.

TODO in smp_cond_load_acquire for architecture:
 - current csky only has:
   lr.w val, <p0>
   sc.w <p0>. val2
   (Any other stores to p0 will let sc.w failed)

 - But smp_cond_load_acquire need:
   lr.w val, <p0>
   wfe
   (Any stores to p0 will send the event to let wfe retired)

Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
Link: https://lore.kernel.org/linux-riscv/CAAhSdy1JHLUFwu7RuCaQ+RUWRBks2KsDva7EpRt8--4ZfofSUQ@mail.gmail.com/T/#m13adac285b7f51f4f879a5d6b65753ecb1a7524e
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Arnd Bergmann <arnd@...db.de>
---
 arch/csky/include/asm/spinlock.h | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/arch/csky/include/asm/spinlock.h b/arch/csky/include/asm/spinlock.h
index 69f5aa249c5f..69677167977a 100644
--- a/arch/csky/include/asm/spinlock.h
+++ b/arch/csky/include/asm/spinlock.h
@@ -26,10 +26,8 @@ static inline void arch_spin_lock(arch_spinlock_t *lock)
 		: "r"(p), "r"(ticket_next)
 		: "cc");
 
-	while (lockval.tickets.next != lockval.tickets.owner)
-		lockval.tickets.owner = READ_ONCE(lock->tickets.owner);
-
-	smp_mb();
+	smp_cond_load_acquire(&lock->tickets.owner,
+					VAL == lockval.tickets.next);
 }
 
 static inline int arch_spin_trylock(arch_spinlock_t *lock)
@@ -55,15 +53,14 @@ static inline int arch_spin_trylock(arch_spinlock_t *lock)
 	} while (!res);
 
 	if (!contended)
-		smp_mb();
+		__smp_acquire_fence();
 
 	return !contended;
 }
 
 static inline void arch_spin_unlock(arch_spinlock_t *lock)
 {
-	smp_mb();
-	WRITE_ONCE(lock->tickets.owner, lock->tickets.owner + 1);
+	smp_store_release(&lock->tickets.owner, lock->tickets.owner + 1);
 }
 
 static inline int arch_spin_value_unlocked(arch_spinlock_t lock)
-- 
2.17.1