Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

Ingo Molnar
2017-03-28T09:52:31Z

* Peter Zijlstra <peterz@infradead.org> wrote:

> On Tue, Mar 28, 2017 at 09:52:32AM +0200, Ingo Molnar wrote:
>
> > No, regular C code.
> >
> > I don't see the point of generating all this code via CPP - it's certainly not
> > making it more readable to me. I.e. this patch I commented on is a step backwards
> > for readability.
>
> Note that much of the atomic stuff we have today is all CPP already.

Yeah, but there it's implementational: we pick up arch primitives depending on
whether they are defined, such as:

#ifndef atomic_read_acquire
# define atomic_read_acquire(v) smp_load_acquire(&(v)->counter)
#endif

> x86 is the exception because its 'weird', but most other archs are
> almost pure CPP -- check Alpha for example, or asm-generic/atomic.h.

include/asm-generic/atomic.h looks pretty clean and readable overall.

> Also, look at linux/atomic.h, its a giant maze of CPP.

Nah, that's OK, much of is is essentially __weak inlines implemented via CPP -
i.e. CPP is filling in a missing compiler feature.

But this patch I replied to appears to add instrumentation wrappery via CPP which
looks like excessive and avoidable obfuscation to me.

If it's much more readable and much more compact than the C version then maybe,
but I'd like to see the C version first and see ...

> The CPP help us generate functions, reduces endless copy/paste (which induces
> random differences -- read bugs) and construct variants depending on the
> architecture input.
>
> Yes, the CPP is a pain, but writing all that out explicitly is more of a
> pain.

So I'm not convinced that it's true in this case.

Could we see the C version and compare? I could be wrong about it all.

Thanks,

Ingo