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Relaxed is OK if the target is a single-core device

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for a multi-core device AcqRel ordering for the fetch-add operation and Release
ordering for the store operation would have been required for correctness
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Jorge Aparicio
2018-11-05 00:50:19 +01:00
parent 5abb337651
commit 691206d763
1 changed files with 6 additions and 7 deletions
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src/concurrency/concurrency.md
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@@ -192,13 +192,12 @@ main thread without disabling interrupts. When possible, this is a better
solution — but it may not be supported on your platform.
A note on [`Ordering`]: this affects how the compiler and hardware may reorder
instructions, and also has consequences on cache visibility. For simple atomic
operations like incrementing a counter, where we are not synchronising any
other tasks on the counter, `Relaxed` is sufficient, and will have the best
performance on typical embedded platforms. Stricter ordering will cause the
compiler to emit memory barriers around the atomic operations; depending on
what you're using atomics for you may or may not need this! The precise
details of the atomic model are complicated and best described elsewhere.
instructions, and also has consequences on cache visibility. Assuming that the
target is a single core platform `Relaxed` is sufficient and the most efficient
choice in this particular case. Stricter ordering will cause the compiler to
emit memory barriers around the atomic operations; depending on what you're
using atomics for you may or may not need this! The precise details of the
atomic model are complicated and best described elsewhere.
For more details on atomics and ordering, see the [nomicon].