arc_usr_cmpxchg and preemption

[Peter Zijlstra]

On Thu, Mar 15, 2018 at 09:12:09AM +0000, Alexey Brodkin wrote:
> On Thu, 2018-03-15 at 09:18 +0100, Peter Zijlstra wrote:

> > Also, it might make sense to stuff this implementation in some lib/ file
> > somewhere and make all platforms that need it use the same code, afaict
> > there really isn't anything platform specific to it.
> 
> Not clear which part do you mean here.
> Are you talking about entire cmpxchg syscall implementation?

Yep.

> Do you think there're many users of that quite an inefficient
> [compared to proper HW version] atomic exchange?

I think there's a bunch of architectures that are in the same boat.
m68k, arm, mips was mentioned. Sure, the moment an arch has hardware
support you don't need the syscall anymore.

I was just thinking it would be good to have a common implementation (if
possible) rather than 4-5 different copies of basically the same thing.