From: Peter Zijlstra <peterz@infradead.org>
To: guoren@kernel.org
Cc: palmer@rivosinc.com, arnd@arndb.de, mingo@redhat.com,
will@kernel.org, longman@redhat.com, boqun.feng@gmail.com,
linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org,
linux-kernel@vger.kernel.org, Guo Ren <guoren@linux.alibaba.com>
Subject: Re: [PATCH V7 1/5] asm-generic: ticket-lock: Remove unnecessary atomic_read
Date: Mon, 4 Jul 2022 11:52:39 +0200 [thread overview]
Message-ID: <YsK4Z9w0tFtgkni8@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20220628081707.1997728-2-guoren@kernel.org>
On Tue, Jun 28, 2022 at 04:17:03AM -0400, guoren@kernel.org wrote:
> From: Guo Ren <guoren@linux.alibaba.com>
>
> Remove unnecessary atomic_read in arch_spin_value_unlocked(lock),
> because the value has been in lock. This patch could prevent
> arch_spin_value_unlocked contend spin_lock data again.
>
> Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@kernel.org>
> Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Palmer Dabbelt <palmer@rivosinc.com>
> ---
> include/asm-generic/spinlock.h | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/include/asm-generic/spinlock.h b/include/asm-generic/spinlock.h
> index fdfebcb050f4..f1e4fa100f5a 100644
> --- a/include/asm-generic/spinlock.h
> +++ b/include/asm-generic/spinlock.h
> @@ -84,7 +84,9 @@ static __always_inline int arch_spin_is_contended(arch_spinlock_t *lock)
>
> static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
> {
> - return !arch_spin_is_locked(&lock);
> + u32 val = lock.counter;
> +
> + return ((val >> 16) == (val & 0xffff));
> }
Wouldn't the right thing be to flip arch_spin_is_locked() and
arch_spin_value_is_unlocked() ?
diff --git a/include/asm-generic/spinlock.h b/include/asm-generic/spinlock.h
index fdfebcb050f4..63ab4da262f2 100644
--- a/include/asm-generic/spinlock.h
+++ b/include/asm-generic/spinlock.h
@@ -68,23 +68,25 @@ static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
smp_store_release(ptr, (u16)val + 1);
}
-static __always_inline int arch_spin_is_locked(arch_spinlock_t *lock)
+static __always_inline int arch_spin_is_contended(arch_spinlock_t *lock)
{
u32 val = atomic_read(lock);
- return ((val >> 16) != (val & 0xffff));
+ return (s16)((val >> 16) - (val & 0xffff)) > 1;
}
-static __always_inline int arch_spin_is_contended(arch_spinlock_t *lock)
+static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
{
- u32 val = atomic_read(lock);
+ u32 val = lock.counter;
- return (s16)((val >> 16) - (val & 0xffff)) > 1;
+ return ((val >> 16) == (val & 0xffff));
}
-static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
+static __always_inline int arch_spin_is_locked(arch_spinlock_t *lock)
{
- return !arch_spin_is_locked(&lock);
+ arch_spinlock_t val = READ_ONCE(*lock);
+
+ return !arch_spin_value_unlocked(val);
}
#include <asm/qrwlock.h>
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next prev parent reply other threads:[~2022-07-04 9:52 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-28 8:17 [PATCH V7 0/5] riscv: Add qspinlock support with combo style guoren
2022-06-28 8:17 ` [PATCH V7 1/5] asm-generic: ticket-lock: Remove unnecessary atomic_read guoren
2022-06-28 18:05 ` Waiman Long
2022-06-29 2:12 ` Guo Ren
2022-06-29 8:27 ` David Laight
2022-07-01 15:18 ` Guo Ren
2022-07-04 9:52 ` Peter Zijlstra [this message]
2022-07-04 11:10 ` Guo Ren
2022-06-28 8:17 ` [PATCH V7 2/5] asm-generic: ticket-lock: Use the same struct definitions with qspinlock guoren
2022-06-28 8:17 ` [PATCH V7 3/5] asm-generic: ticket-lock: Move into ticket_spinlock.h guoren
2022-06-28 8:17 ` [PATCH V7 4/5] asm-generic: spinlock: Add combo spinlock (ticket & queued) guoren
2022-06-28 18:13 ` Waiman Long
2022-06-29 1:17 ` Guo Ren
2022-06-29 1:34 ` Waiman Long
2022-06-29 2:29 ` Guo Ren
2022-06-29 7:08 ` Arnd Bergmann
2022-06-29 8:24 ` Guo Ren
2022-06-29 8:29 ` Arnd Bergmann
2022-07-01 12:18 ` Guo Ren
2022-06-29 12:53 ` Waiman Long
2022-07-04 9:57 ` Peter Zijlstra
2022-07-04 13:13 ` Guo Ren
2022-07-04 13:45 ` Peter Zijlstra
2022-06-28 8:17 ` [PATCH V7 5/5] riscv: Add qspinlock support guoren
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