[PATCH] powerpc/8xx: fix regression introduced by cache coherency rewrite

[Rex Feany]

Thus spake Benjamin Herrenschmidt (benh at kernel.crashing.org):

> On Thu, 2009-09-24 at 18:35 -0700, Rex Feany wrote:
> > 
> > Then I can boot and get to a shell, but userspace is slow. 8 seconds
> > to mount
> > /proc (vs. less then a second using my old kernel)! Maybe this is an
> > unrelated issue?  I'm pretty clueless about the details, I'm sorry.
> > PG_arch_1 is used to prevent a cache flush unless it is actually
> > needed?
> > Then why would changing the location of the tlbil_va() make a
> > difference?
> 
> I think there's more finishyness to 8xx than we thought. IE. That
> tlbil_va might have more reasons to be there than what the comment
> seems to advertize. Can you try to move it even higher up ? IE.
> Unconditionally at the beginning of set_pte_filter ?
> 
> Also, if that doesn't help, can you try putting one in
> set_access_flags_filter() just below ?
> 
> (Beware that there's two different versions of both functions, only the
> first one is compiled/used on 8xx).
> 
> It's going to be hard for me to get that "right" since I don't really
> know what's going on with the core here, but I suppose if we get it
> moving along with extra tlb invalidations, that should be "good enough"
> until somebody who really knows what's going on comes up with possibly
> a better fix.

I've tried sticking tlbil_va() in those places, nothing seems to help.
In some cases userspace is slow, in other cases userspace is faster and
unstable: sometimes commands hang, sometimes I am able to ctrl-c and
and kill it, sometimes I get other strange crashes or falures (so far no
kernel oopses though).

take care!
/rex.