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Date: Mon, 2 Nov 2015 13:45:57 +0100
From: Jan Viktorin <viktorin@rehivetech.com>
To: "Hunt, David" <david.hunt@intel.com>
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Subject: Re: [dpdk-dev] [PATCH v3 1/6] eal/arm: add 64-bit armv8 version of
 rte_memcpy.h
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On Mon, 2 Nov 2015 12:22:47 +0000
"Hunt, David" <david.hunt@intel.com> wrote:

> On 02/11/2015 04:57, Jerin Jacob wrote:
> > On Fri, Oct 30, 2015 at 01:49:14PM +0000, David Hunt wrote:  
> >> Signed-off-by: David Hunt <david.hunt@intel.com>  
> --snip--
> >> +#ifndef _RTE_MEMCPY_ARM_64_H_
> >> +#define _RTE_MEMCPY_ARM_64_H_
> >> +
> >> +#include <stdint.h>
> >> +#include <string.h>
> >> +
> >> +#ifdef __cplusplus
> >> +extern "C" {
> >> +#endif
> >> +
> >> +#include "generic/rte_memcpy.h"
> >> +
> >> +#ifdef __ARM_NEON_FP  
> >
> > SIMD is not optional in armv8 spec.So every armv8 machine will have
> > SIMD instruction unlike armv7.More over LDP/STP instruction is
> > not part of SIMD.So this check is not required or it can
> > be replaced with a check that select memcpy from either libc or this specific
> > implementation  
> 
> Jerin,
>     I've just benchmarked the libc version against the hand-coded 
> version of the memcpy routines, and the libc wins in most cases. This 
> code was just an initial attempt at optimising the memccpy's, so I feel 
> that with the current benchmark results, it would better just to remove 
> the assembly versions, and use the libc version for the initial release 
> on ARMv8.
> Then, in the future, the ARMv8 experts are free to submit an optimised 
> version as a patch in the future. Does that sound reasonable to you?
> Rgds,
> Dave.

As there is no use of NEON in the code, this optimization seems to be
useless to me...

Jan

> 
> 
> --snip--
> 
> 
> 



-- 
   Jan Viktorin                  E-mail: Viktorin@RehiveTech.com
   System Architect              Web:    www.RehiveTech.com
   RehiveTech
   Brno, Czech Republic