Re: PREEMPT for ppc64

[Linus Torvalds <torvalds@osdl.org>]

On Mon, 7 Jun 2004, Paul Mackerras wrote:
>
> Here is a patch that implements CONFIG_PREEMPT for ppc64.  Aside from
> the entry.S changes to check the _TIF_NEED_RESCHED bit when returning
> from an exception, most of the changes are to add preempt/{dis,en}able
> in various places.  Undoubtedly I have missed some though.

I would really suggest you push these into the "enable_kernel_fp()" thing, 
for example, rather than open-coding them. Also, code like

	+     preempt_disable();
	      if (regs->msr & MSR_VEC)
	              giveup_altivec(current);
	+     preempt_enable();

doesn't seem to make much sense, since "regs->msr" certainly isn't 
changing, so clearly the above is equivalent to just pushing the whole 
preempt disable into "giveup_altivec()".

The most _common_ bug (and the one I don't see any code for at all in your
patch) is stuff that knows which CPU it is on, or that reads actual
special CPU registers and acts on them. The other thing to look out for is
anything that gets the CPU number: use "get_cpu() + put_cpu()" rather than
"smp_processor_id()".

		Linus