On 11/13/2015 09:22 AM, Frederic Weisbecker wrote:
Export fetch_or() that's implemented and used internally by the
scheduler. We are going to use it for NO_HZ so make it generally
available.
Cc: Christoph Lameter<[email protected]>
Cc: Chris Metcalf<[email protected]>
Cc: Ingo Molnar<[email protected]>
Cc: Luiz Capitulino<[email protected]>
Cc: Peter Zijlstra<[email protected]>
Cc: Rik van Riel<[email protected]>
Cc: Thomas Gleixner<[email protected]>
Cc: Viresh Kumar<[email protected]>
Signed-off-by: Frederic Weisbecker<[email protected]>
---
include/linux/atomic.h | 18 ++++++++++++++++++
kernel/sched/core.c | 14 --------------
2 files changed, 18 insertions(+), 14 deletions(-)
diff --git a/include/linux/atomic.h b/include/linux/atomic.h
index 00a5763..c3b99f8 100644
--- a/include/linux/atomic.h
+++ b/include/linux/atomic.h
@@ -451,6 +451,24 @@ static inline int atomic_dec_if_positive(atomic_t *v)
}
#endif
+/**
+ * fetch_or - perform *ptr |= mask and return old value of *ptr
+ * @ptr: pointer to value
+ * @mask: mask to OR on the value
+ *
+ * cmpxchg based fetch_or, macro so it works for different integer types
+ */
+#define fetch_or(ptr, mask) \
+({ typeof(*(ptr)) __old, __val = *(ptr); \
+ for (;;) { \
+ __old = cmpxchg((ptr), __val, __val | (mask)); \
+ if (__old == __val) \
+ break; \
+ __val = __old; \
+ } \
+ __old; \
+})
+
#include <asm-generic/atomic-long.h>
#ifdef CONFIG_GENERIC_ATOMIC64
#include <asm-generic/atomic64.h>
I think this should be guarded by an "#ifndef" like other things in
this file, so architectures can provide their own implementations,
or can use the C11 atomic_fetch_or() for newer compilers.
Also, I wonder about the nomenclature here: other than cmpxchg
and xchg, all the atomic ops are named "atomic_xxx". For something
that returns the old value, I'd expect it to be atomic_or_return()
and be otherwise like the existing atomic_or() routine, and thus you'd
specify "atomic_t tick_dependency".
Avoiding all of these issues is probably why fetch_or() is not exported :-)
I made some similar comments last time around:
https://lkml.kernel.org/r/[email protected]
--
Chris Metcalf, EZChip Semiconductor
http://www.ezchip.com
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