Re: [PATCH 1/2] powerpc: string: implement optimized memset variants

["Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>]

On 2017/03/28 11:44AM, Michael Ellerman wrote:
> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> writes:
> 
> > diff --git a/arch/powerpc/lib/mem_64.S b/arch/powerpc/lib/mem_64.S
> > index 85fa9869aec5..ec531de99996 100644
> > --- a/arch/powerpc/lib/mem_64.S
> > +++ b/arch/powerpc/lib/mem_64.S
> > @@ -13,6 +13,23 @@
> >  #include <asm/ppc_asm.h>
> >  #include <asm/export.h>
> >  
> > +_GLOBAL(__memset16)
> > +	rlwimi	r4,r4,16,0,15
> > +	/* fall through */
> > +
> > +_GLOBAL(__memset32)
> > +	rldimi	r4,r4,32,0
> > +	/* fall through */
> > +
> > +_GLOBAL(__memset64)
> > +	neg	r0,r3
> > +	andi.	r0,r0,7
> > +	cmplw	cr1,r5,r0
> > +	b	.Lms
> > +EXPORT_SYMBOL(__memset16)
> > +EXPORT_SYMBOL(__memset32)
> > +EXPORT_SYMBOL(__memset64)
> 
> You'll have to convince me that's better than what GCC produces.

Sure :) I got lazy yesterday night and didn't post the test results...

I hadn't tested zram yesterday, but only done tests with a naive test 
module that memset's a large 1GB buffer with integers. With that test, I 
saw:

without patch:       0.389253910 seconds time elapsed    ( +-  1.49% )
with patch:          0.173269267 seconds time elapsed    ( +-  1.55% )

.. which is better than 2x.

I also tested zram today with the command shared by Wilcox:

without patch:       1.493782568 seconds time elapsed    ( +-  0.08% )
with patch:          1.408457577 seconds time elapsed    ( +-  0.15% )

... which also shows an improvement along the same lines as x86, as 
reported by Minchan Kim.


- Naveen