A few other cache related optimizations for Cortex-A9.

[Russell King - ARM Linux]

On Wed, Jul 06, 2011 at 09:56:56AM +0100, Catalin Marinas wrote:
> On Wed, Jul 06, 2011 at 04:14:57AM +0100, heechul Yun wrote:
> > I found a few other places which, I believe, are not necessary for Cortex-A9.
> > 
> > diff --git a/arch/arm/mm/copypage-v6.c b/arch/arm/mm/copypage-v6.c
> > index bdba6c6..6d5a847 100644
> > --- a/arch/arm/mm/copypage-v6.c
> > +++ b/arch/arm/mm/copypage-v6.c
> > @@ -41,7 +41,9 @@ static void v6_copy_user_highpage_nonaliasing(struct page *to,
> >         kfrom = kmap_atomic(from, KM_USER0);
> >         kto = kmap_atomic(to, KM_USER1);
> >         copy_page(kto, kfrom);
> > +#ifndef CONFIG_CPU_CACHE_V7
> >         __cpuc_flush_dcache_area(kto, PAGE_SIZE);
> > +#endif
> >         kunmap_atomic(kto, KM_USER1);
> >         kunmap_atomic(kfrom, KM_USER0);
> >  }
> > 
> > On handling COW page fault, the above function is called to copy the
> > page content of the parent to a newly allocate page frame for the
> > child. Again, since D cache of A9 is PIPT, we do not need to flush the
> > page as in x86. This modification improves lmbench (fork/exec/shell)
> > performance by 4-6%.
> 
> See commit 115b2247 introducing this. We indeed have a PIPT like cache
> on A9 but it is a Harvard architecture with separate I and D caches. It
> happened in the past that we got a COW for text page and the I and D
> cache became incoherent. Since then, the dynamic linker has been fixed
> and no longer causes this. We could add a check for VM_EXEC in
> vma->vm_flags.
> 
> But I wonder whether we still need this flush after commit c0177800
> where we assume that a new page cache page has dirty D-cache (and we
> later flush the caches via set_pte_at).

I don't think we need that flush there after c0177800 either.  I/D
coherency implies that pte_exec() is set, which will get us through
to the checking of PG_arch_1 in __sync_icache_dcache(), where we'll
call __flush_dcache_page for this page.

We don't need this flush anymore, so let's simply kill it outright.

Heechul (sorry, is that the correct way of addressing you?) could
you please submit a patch removing the __cpuc_flush_dcache_area()
from v6_copy_user_highpage_nonaliasing() entirely please?

Thanks.