On 6/21/23 20:53, Olivier Dion wrote:
On Wed, 21 Jun 2023, "Paul E. McKenney" <paul...@kernel.org> wrote:
On Mon, May 15, 2023 at 04:17:11PM -0400, Olivier Dion wrote:
#ifndef cmm_mb
#define cmm_mb() __sync_synchronize()
Just out of curiosity, why not also implement cmm_mb() in terms of
__atomic_thread_fence(__ATOMIC_SEQ_CST)? (Or is that a later patch?)
IIRC, Mathieu and I agree that the definition of a thread fence -- acts
as a synchronization fence between threads -- is too weak for what we
want here. For example, with I/O devices.
Although __sync_synchronize() is probably an alias for a SEQ_CST thread
fence, its definition -- issues a full memory barrier -- is stronger.
We do not want to rely on this assumption (alias) and prefer to rely on
the documented definition instead.
We should document this rationale with a new comment near the #define,
in case anyone mistakenly decides to use a thread fence there to make it
similar to the rest of the code in the future.
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
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