mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-11-16 06:35:39 +08:00
706eeb3e9c
Since we've vastly expanded the atomic_t interface in recent years the existing documentation is woefully out of date and people seem to get confused a bit. Start a new document to hopefully better explain the current state of affairs. The old atomic_ops.txt also covers bitmaps and a few more details so this is not a full replacement and we'll therefore keep that document around until such a time that we've managed to write more text to cover its entire. Also please, ReST people, go away. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will.deacon@arm.com> Signed-off-by: Ingo Molnar <mingo@kernel.org>
67 lines
1.3 KiB
Plaintext
67 lines
1.3 KiB
Plaintext
|
|
On atomic bitops.
|
|
|
|
|
|
While our bitmap_{}() functions are non-atomic, we have a number of operations
|
|
operating on single bits in a bitmap that are atomic.
|
|
|
|
|
|
API
|
|
---
|
|
|
|
The single bit operations are:
|
|
|
|
Non-RMW ops:
|
|
|
|
test_bit()
|
|
|
|
RMW atomic operations without return value:
|
|
|
|
{set,clear,change}_bit()
|
|
clear_bit_unlock()
|
|
|
|
RMW atomic operations with return value:
|
|
|
|
test_and_{set,clear,change}_bit()
|
|
test_and_set_bit_lock()
|
|
|
|
Barriers:
|
|
|
|
smp_mb__{before,after}_atomic()
|
|
|
|
|
|
All RMW atomic operations have a '__' prefixed variant which is non-atomic.
|
|
|
|
|
|
SEMANTICS
|
|
---------
|
|
|
|
Non-atomic ops:
|
|
|
|
In particular __clear_bit_unlock() suffers the same issue as atomic_set(),
|
|
which is why the generic version maps to clear_bit_unlock(), see atomic_t.txt.
|
|
|
|
|
|
RMW ops:
|
|
|
|
The test_and_{}_bit() operations return the original value of the bit.
|
|
|
|
|
|
ORDERING
|
|
--------
|
|
|
|
Like with atomic_t, the rule of thumb is:
|
|
|
|
- non-RMW operations are unordered;
|
|
|
|
- RMW operations that have no return value are unordered;
|
|
|
|
- RMW operations that have a return value are fully ordered.
|
|
|
|
Except for test_and_set_bit_lock() which has ACQUIRE semantics and
|
|
clear_bit_unlock() which has RELEASE semantics.
|
|
|
|
Since a platform only has a single means of achieving atomic operations
|
|
the same barriers as for atomic_t are used, see atomic_t.txt.
|
|
|