Re: [PATCH] Futexes IV (Fast Lightweight Userspace Semaphores)

Linus Torvalds
2002-03-08T21:03:44Z

On Fri, 8 Mar 2002, Hubertus Franke wrote:
>
> But what about compatibility with i368, no cmpxchg or cmpxchg8b
> Can't we have to types and infer from the op in the kernel what
> the correct size in user space is.

I think the next step should be to map in one page of kernel code in a
user-readable location, and just do it there.

It's not just 386 vs later due to cmpxchg. It's also the simple issue of
UP vs SMP - a UP system still wants to do locking, but it doesn't need the
lock prefix. And that lock prefix makes a _huge_ difference
performance-wise.

So my suggestion is: ignore i386 for now (no _relevant_ SMP boxes exist
anyway), and plan on solving the problem with a separate library page
before 2.6.x gets released.

Linus