Re: [RFC] LKMM: Add volatile_if()

Linus Torvalds
2021-06-04T16:30:23Z

On Fri, Jun 4, 2021 at 3:12 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> I've converted most architectures we care about, and the rest will get
> an extra smp_mb() by means of the 'generic' fallback implementation (for
> now).

Why is "volatile_if()" not just

#define barier_true() ({ barrier(); 1; })

#define volatile_if(x) if ((x) && barrier_true())

because that should essentially cause the same thing - the compiler
should be *forced* to create one conditional branch (because "barrier"
is an asm that can't be done on the false side, so it can't do it with
arithmetic or other games), and after that we're done.

No need for per-architecture "asm goto" games. No new memory barriers.
No actual new code generation (except for the empty asm volatile that
is a barrier).

Linus