From: Manfred Spraul <manfred@colorfullife.com>
To: benh@kernel.crashing.org, paulmck@linux.vnet.ibm.com,
Ingo Molnar <mingo@elte.hu>, Boqun Feng <boqun.feng@gmail.com>,
Peter Zijlstra <peterz@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
1vier1@web.de, Davidlohr Bueso <dave@stgolabs.net>,
Manfred Spraul <manfred@colorfullife.com>
Subject: [PATCH 4/4 V4] qspinlock for x86: smp_mb__after_spin_lock() is free
Date: Mon, 29 Aug 2016 15:34:29 +0200 [thread overview]
Message-ID: <1472477669-27508-5-git-send-email-manfred@colorfullife.com> (raw)
In-Reply-To: <1472477669-27508-1-git-send-email-manfred@colorfullife.com>
For x86 qspinlocks, no additional memory barrier is required in
smp_mb__after_spin_lock:
Theoretically, for qspinlock we could define two barriers:
- smp_mb__after_spin_lock: Free for x86, not free for powerpc
- smp_mb__between_spin_lock_and_spin_unlock_wait():
Free for all archs, see queued_spin_unlock_wait for details.
As smp_mb__between_spin_lock_and_spin_unlock_wait() is not used
in any hotpaths, the patch does not create that define yet.
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
---
arch/x86/include/asm/qspinlock.h | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h
index eaba080..04d26ed 100644
--- a/arch/x86/include/asm/qspinlock.h
+++ b/arch/x86/include/asm/qspinlock.h
@@ -61,6 +61,17 @@ static inline bool virt_spin_lock(struct qspinlock *lock)
}
#endif /* CONFIG_PARAVIRT */
+#ifndef smp_mb__after_spin_lock
+/**
+ * smp_mb__after_spin_lock() - Provide smp_mb() after spin_lock
+ *
+ * queued_spin_lock() provides full memory barriers semantics,
+ * thus no further memory barrier is required. See
+ * queued_spin_unlock_wait() for further details.
+ */
+#define smp_mb__after_spin_lock() do { } while (0)
+#endif
+
#include <asm-generic/qspinlock.h>
#endif /* _ASM_X86_QSPINLOCK_H */
--
2.5.5
prev parent reply other threads:[~2016-08-29 13:36 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-29 13:34 [PATCH 0/4 V4] Clarify/standardize memory barriers for lock/unlock Manfred Spraul
2016-08-29 13:34 ` [PATCH 1/4 v4] spinlock: Document memory barrier rules Manfred Spraul
2016-08-29 17:38 ` Davidlohr Bueso
2016-08-29 13:34 ` [PATCH 2/4 V4] spinlock.h: Move smp_mb__after_unlock_lock to spinlock.h Manfred Spraul
2016-08-29 13:34 ` [PATCH 3/4 V4] net/netfilter/nf_conntrack_core: update memory barriers Manfred Spraul
2016-08-29 13:34 ` Manfred Spraul [this message]
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