From: Peter Zijlstra <peterz@infradead.org>
To: linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
manfred@colorfullife.com, dave@stgolabs.net,
paulmck@linux.vnet.ibm.com, will.deacon@arm.com
Cc: boqun.feng@gmail.com, Waiman.Long@hpe.com, tj@kernel.org,
pablo@netfilter.org, kaber@trash.net, davem@davemloft.net,
oleg@redhat.com, netfilter-devel@vger.kernel.org,
sasha.levin@oracle.com, hofrat@osadl.org,
"Peter Zijlstra (Intel)" <peterz@infradead.org>
Subject: [PATCH -v2 2/6] locking: Introduce cmpwait()
Date: Thu, 26 May 2016 16:19:24 +0200 [thread overview]
Message-ID: <20160526142354.150759303@infradead.org> (raw)
In-Reply-To: 20160526141922.163198062@infradead.org
[-- Attachment #1: peterz-locking-cmp_and_wait.patch --]
[-- Type: text/plain, Size: 1481 bytes --]
Provide the cmpwait() primitive, which will 'spin' wait for a variable
to change and use it to implement smp_cond_load_acquire().
This primitive can be implemented with hardware assist on some
platforms (ARM64, x86).
Suggested-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
include/linux/compiler.h | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -305,6 +305,23 @@ static __always_inline void __write_once
})
/**
+ * cmpwait - compare and wait for a variable to change
+ * @ptr: pointer to the variable to wait on
+ * @val: the value it should change from
+ *
+ * A simple constuct that waits for a variable to change from a known
+ * value; some architectures can do this in hardware.
+ */
+#ifndef cmpwait
+#define cmpwait(ptr, val) do { \
+ typeof (ptr) __ptr = (ptr); \
+ typeof (val) __val = (val); \
+ while (READ_ONCE(*__ptr) == __val) \
+ cpu_relax(); \
+} while (0)
+#endif
+
+/**
* smp_cond_load_acquire() - (Spin) wait for cond with ACQUIRE ordering
* @ptr: pointer to the variable to wait on
* @cond: boolean expression to wait for
@@ -327,7 +344,7 @@ static __always_inline void __write_once
VAL = READ_ONCE(*__PTR); \
if (cond_expr) \
break; \
- cpu_relax(); \
+ cmpwait(__PTR, VAL); \
} \
smp_rmb(); /* ctrl + rmb := acquire */ \
VAL; \
next prev parent reply other threads:[~2016-05-26 14:26 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-26 14:19 [PATCH -v2 0/6] spin_unlock_wait borkage Peter Zijlstra
2016-05-26 14:19 ` [PATCH -v2 1/6] locking: Replace smp_cond_acquire with smp_cond_load_acquire Peter Zijlstra
2016-05-26 14:19 ` Peter Zijlstra [this message]
2016-05-26 14:19 ` [PATCH -v2 3/6] locking: Introduce smp_acquire__after_ctrl_dep Peter Zijlstra
2016-05-26 14:19 ` [PATCH -v2 4/6] locking, arch: Update spin_unlock_wait() Peter Zijlstra
2016-05-26 21:10 ` Chris Metcalf
2016-05-27 9:05 ` Peter Zijlstra
2016-05-27 19:34 ` Chris Metcalf
2016-05-30 9:25 ` Peter Zijlstra
2016-05-27 6:46 ` Martin Schwidefsky
2016-05-27 9:02 ` Peter Zijlstra
2016-05-26 14:19 ` [PATCH -v2 5/6] locking: Update spin_unlock_wait users Peter Zijlstra
2016-05-26 14:19 ` [PATCH -v2 6/6] locking,netfilter: Fix nf_conntrack_lock() Peter Zijlstra
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