Now I'm curious...

[Paul Brook]

On Wednesday 05 September 2007, Daniel Jacobowitz wrote:
> On Wed, Sep 05, 2007 at 11:49:12AM -0400, Crane, Matthew wrote:
> > What makes you say it would be useless?  Or that the performance will
> > suck?
>
> I'm curious too.  I wouldn't expect it to work without a bit of
> hacking - I don't know if the futex and atomic bits in the kernel are
> right for no-mmu, and the last time I checked the arm no-mmu port,
> they weren't.  But once that's solved, I would expect it to have the
> same advantages on uClinux that it has on Linux.

Last time I checked (a coupe of months ago) the futex bits should work, TLS 
worked by trapping and emulating a hardware register (very slow) and atomic 
operations weren't supported. So with current kernels it's accurate to say 
that ARM uClinux NPTL won't work, and even the bits that do work will be 
slow.

However I'm fairly sure that all these problems are fixable. We needed 
significant kernel ABI enhancements to make NPTL work on normal linux, so 
it's reasonable to expect the same changes will be required for uClinux.

Saying "use linuxthreads" is ok, if you ignore the fact that noone is really 
maintaining the linuxthreads code, it has some fairly fundamental 
restrictions, doesn't scale particularly well, and probably doesn't work on 
ARM SMP hardware.

Paul