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SubjectRe: [PATCH] locking/atomics: Clean up the atomic.h maze of #defines

* 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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