Messages in this thread |  | | Date | Sat, 5 May 2018 11:04:03 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] locking/atomics: Clean up the atomic.h maze of #defines |
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* Peter Zijlstra <peterz@infradead.org> wrote:
> > So we could do the following simplification on top of that: > > > > #ifndef atomic_fetch_dec_relaxed > > # ifndef atomic_fetch_dec > > # define atomic_fetch_dec(v) atomic_fetch_sub(1, (v)) > > # define atomic_fetch_dec_relaxed(v) atomic_fetch_sub_relaxed(1, (v)) > > # define atomic_fetch_dec_acquire(v) atomic_fetch_sub_acquire(1, (v)) > > # define atomic_fetch_dec_release(v) atomic_fetch_sub_release(1, (v)) > > # else > > # define atomic_fetch_dec_relaxed atomic_fetch_dec > > # define atomic_fetch_dec_acquire atomic_fetch_dec > > # define atomic_fetch_dec_release atomic_fetch_dec > > # endif > > #else > > # ifndef atomic_fetch_dec > > # define atomic_fetch_dec(...) __atomic_op_fence(atomic_fetch_dec, __VA_ARGS__) > > # define atomic_fetch_dec_acquire(...) __atomic_op_acquire(atomic_fetch_dec, __VA_ARGS__) > > # define atomic_fetch_dec_release(...) __atomic_op_release(atomic_fetch_dec, __VA_ARGS__) > > # endif > > #endif > > This would disallow an architecture to override just fetch_dec_release for > instance.
Couldn't such a crazy arch just define _all_ the 3 APIs in this group? That's really a small price and makes the place pay the complexity price that does the weirdness...
> I don't think there currently is any architecture that does that, but the > intent was to allow it to override anything and only provide defaults where it > does not.
I'd argue that if a new arch only defines one of these APIs that's probably a bug. If they absolutely want to do it, they still can - by defining all 3 APIs.
So there's no loss in arch flexibility.
> None of this takes away the giant trainwreck that is the annotated atomic stuff > though. > > And I seriously hate this one: > > ba1c9f83f633 ("locking/atomic/x86: Un-macro-ify atomic ops implementation") > > and will likely undo that the moment I need to change anything there.
If it makes the code more readable then I don't object - the problem was that the instrumentation indirection made all that code much harder to follow.
Thanks,
Ingo
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