Re: [PATCH v2 22/25] powerpc32: move xxxxx_dcache_range() functions inline

[Joakim Tjernlund <joakim.tjernlund@transmode.se>]

On Tue, 2015-09-22 at 15:14 -0500, Scott Wood wrote:
> On Tue, 2015-09-22 at 19:55 +0000, Joakim Tjernlund wrote:
> > On Tue, 2015-09-22 at 14:42 -0500, Scott Wood wrote:
> > > On Tue, 2015-09-22 at 19:34 +0000, Joakim Tjernlund wrote:
> > > > On Tue, 2015-09-22 at 13:58 -0500, Scott Wood wrote:
> > > > > On Tue, 2015-09-22 at 18:12 +0000, Joakim Tjernlund wrote:
> > > > > > On Tue, 2015-09-22 at 18:51 +0200, Christophe Leroy wrote:
> > > > > > > flush/clean/invalidate _dcache_range() functions are all very
> > > > > > > similar and are quite short. They are mainly used in __dma_sy=
nc()
> > > > > > > perf_event locate them in the top 3 consumming functions duri=
ng
> > > > > > > heavy ethernet activity
> > > > > > >=20
> > > > > > > They are good candidate for inlining, as __dma_sync() does
> > > > > > > almost nothing but calling them
> > > > > > >=20
> > > > > > > Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> > > > > > > ---
> > > > > > > New in v2
> > > > > > >=20
> > > > > > >  arch/powerpc/include/asm/cacheflush.h | 55=20
> > > > > > > +++++++++++++++++++++++++++--
> > > > > > >  arch/powerpc/kernel/misc_32.S         | 65 -----------------=
-----
> > > > > > > ----
> > > > > > > ----
> > > > > > > -----
> > > > > > >  arch/powerpc/kernel/ppc_ksyms.c       |  2 ++
> > > > > > >  3 files changed, 54 insertions(+), 68 deletions(-)
> > > > > > >=20
> > > > > > > diff --git a/arch/powerpc/include/asm/cacheflush.h=20
> > > > > > > b/arch/powerpc/include/asm/cacheflush.h
> > > > > > > index 6229e6b..6169604 100644
> > > > > > > --- a/arch/powerpc/include/asm/cacheflush.h
> > > > > > > +++ b/arch/powerpc/include/asm/cacheflush.h
> > > > > > > @@ -47,12 +47,61 @@ static inline void=20
> > > > > > > __flush_dcache_icache_phys(unsigned long physaddr)
> > > > > > >  }
> > > > > > >  #endif
> > > > > > > =20
> > > > > > > -extern void flush_dcache_range(unsigned long start, unsigned=
=20
> > > > > > > long=20
> > > > > > > stop);
> > > > > > >  #ifdef CONFIG_PPC32
> > > > > > > -extern void clean_dcache_range(unsigned long start, unsigned=
=20
> > > > > > > long=20
> > > > > > > stop);
> > > > > > > -extern void invalidate_dcache_range(unsigned long start,=20
> > > > > > > unsigned=20
> > > > > > > long=20
> > > > > > > stop);
> > > > > > > +/*
> > > > > > > + * Write any modified data cache blocks out to memory and=20
> > > > > > > invalidate=20
> > > > > > > them.
> > > > > > > + * Does not invalidate the corresponding instruction cache=20
> > > > > > > blocks.
> > > > > > > + */
> > > > > > > +static inline void flush_dcache_range(unsigned long start,=20
> > > > > > > unsigned=20
> > > > > > > long=20
> > > > > > > stop)
> > > > > > > +{
> > > > > > > +   void *addr =3D (void *)(start & ~(L1_CACHE_BYTES - 1));
> > > > > > > +   unsigned int size =3D stop - (unsigned long)addr +=20
> > > > > > > (L1_CACHE_BYTES -
> > > > > > > 1);
> > > > > > > +   unsigned int i;
> > > > > > > +
> > > > > > > +   for (i =3D 0; i < size >> L1_CACHE_SHIFT; i++, addr +=3D=
=20
> > > > > > > L1_CACHE_BYTES)
> > > > > > > +           dcbf(addr);
> > > > > > > +   if (i)
> > > > > > > +           mb();   /* sync */
> > > > > > > +}
> > > > > >=20
> > > > > > This feels optimized for the uncommon case when there is no=20
> > > > > > invalidation.
> > > > >=20
> > > > > If you mean the "if (i)", yes, that looks odd.
> > > >=20
> > > > Yes.
> > > >=20
> > > > >=20
> > > > > > I THINK it would be better to bail early=20
> > > > >=20
> > > > > Bail under what conditions?
> > > >=20
> > > > test for "i =3D 0" and return.=20
> > >=20
> > > Why bother?
> >=20
> > I usally find it better to dela with special cases upfront s=E5 the res=
t=20
> > doesn't need to
> > bother. i=3D0 is a NOP and it is clearer to show that upfront.
>=20
> No, I mean why bother special casing this at all?

I just said why?=20
You to found the if(i) mb() a bit odd and it took a little time to see why =
it was there.
Ahh, you mean just skip the if(i) and have mb() unconditionally?
That changes the semantics a little from the ASM version but perhaps that d=
oesn't matter?=