Re: [PATCH v5 3/3] powerpc/lib: optimise PPC32 memcmp

[Christophe LEROY]

Le 29/05/2018 Ã 22:03, Mathieu Malaterre a ÃcritÂ:
> On Mon, May 28, 2018 at 12:49 PM, Christophe Leroy
> <christophe.leroy@xxxxxx> wrote:
> > At the time being, memcmp() compares two chunks of memory
> > byte per byte.
> >
> > This patch optimises the comparison by comparing word by word.
> >
> > A small benchmark performed on an 8xx comparing two chuncks
> > of 512 bytes performed 100000 times gives:
> >
> > Before : 5852274 TB ticks
> > After:   1488638 TB ticks
> >
> > This is almost 4 times faster
> >
> > Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
> > ---
> >   arch/powerpc/lib/string_32.S | 37 +++++++++++++++++++++++++++----------
> >   1 file changed, 27 insertions(+), 10 deletions(-)
>
> Would it possible for you to move the actual code instead to:
>
> ./arch/powerpc/lib/memcmp_32.S
>
> This will seat right next to memcmp_64.S implementation.

Good idea, thanks.
Done in v6

Christophe

> > diff --git a/arch/powerpc/lib/string_32.S b/arch/powerpc/lib/string_32.S
> > index 40a576d56ac7..4fbaa046aa84 100644
> > --- a/arch/powerpc/lib/string_32.S
> > +++ b/arch/powerpc/lib/string_32.S
> > @@ -16,17 +16,34 @@
> >          .text
> >
> >   _GLOBAL(memcmp)
> > -       cmpwi   cr0, r5, 0
> > -       beq-    2f
> > -       mtctr   r5
> > -       addi    r6,r3,-1
> > -       addi    r4,r4,-1
> > -1:     lbzu    r3,1(r6)
> > -       lbzu    r0,1(r4)
> > -       subf.   r3,r0,r3
> > -       bdnzt   2,1b
> > +       srawi.  r7, r5, 2               /* Divide len by 4 */
> > +       mr      r6, r3
> > +       beq-    3f
> > +       mtctr   r7
> > +       li      r7, 0
> > +1:     lwzx    r3, r6, r7
> > +       lwzx    r0, r4, r7
> > +       addi    r7, r7, 4
> > +       cmplw   cr0, r3, r0
> > +       bdnzt   eq, 1b
> > +       bne     5f
> > +3:     andi.   r3, r5, 3
> > +       beqlr
> > +       cmplwi  cr1, r3, 2
> > +       blt-    cr1, 4f
> > +       lhzx    r3, r6, r7
> > +       lhzx    r0, r4, r7
> > +       addi    r7, r7, 2
> > +       subf.   r3, r0, r3
> > +       beqlr   cr1
> > +       bnelr
> > +4:     lbzx    r3, r6, r7
> > +       lbzx    r0, r4, r7
> > +       subf.   r3, r0, r3
> >          blr
> > -2:     li      r3,0
> > +5:     li      r3, 1
> > +       bgtlr
> > +       li      r3, -1
> >          blr
> >   EXPORT_SYMBOL(memcmp)
> >
> > --
> > 2.13.3