[dpdk-dev] [PATCH v4 3/5] hash: add fallback to software CRC32 implementation

[Neil Horman]

On Tue, Nov 18, 2014 at 11:13:17PM +0600, Yerden Zhumabekov wrote:
> 
> 18.11.2014 22:00, Neil Horman пишет:
> > On Tue, Nov 18, 2014 at 09:06:35PM +0600, Yerden Zhumabekov wrote:
> >> 18.11.2014 20:41, Neil Horman пишет:
> >>> On Tue, Nov 18, 2014 at 08:03:40PM +0600, Yerden Zhumabekov wrote:
> >>>>  /**
> >>>>   * Use single crc32 instruction to perform a hash on a 4 byte value.
> >>>> + * Fall back to software crc32 implementation in case SSE4.2 is
> >>>> + * not supported
> >>>>   *
> >>>>   * @param data
> >>>>   *   Data to perform hash on.
> >>>> @@ -376,11 +413,18 @@ crc32c_2words(uint64_t data, uint32_t init_val)
> >>>>  static inline uint32_t
> >>>>  rte_hash_crc_4byte(uint32_t data, uint32_t init_val)
> >>>>  {
> >>>> -	return _mm_crc32_u32(init_val, data);
> >>>> +#ifdef RTE_MACHINE_CPUFLAG_SSE4_2
> >>>> +	if (likely(crc32_alg == CRC32_SSE42))
> >>>> +		return _mm_crc32_u32(init_val, data);
> >>>> +#endif
> >>> you don't really need these ifdefs here anymore given that you have a
> >>> constructor to do the algorithm selection.  In fact you need to remove them, in
> >>> the event you build on a system that doesn't support SSE42, but run on a system
> >>> that does.
> >> Originally, I thought so as well. I wrote the code without these ifdefs,
> >> but it didn't compile on my machine which doesn't support SSE4.2. Error
> >> was triggered by nmmintrin.h which has a check for respective GCC
> >> extension. So I think these ifdefs are indeed required.
> >>
> > You need to edit the makefile so that the compiler gets passed the option
> > -msse42.  That way it will know to emit sse42 instructions. It will also allow
> > you to remove the ifdef from the include file
> 
> In this case, I guess there are two options:
> 1) modify all makefiles which use librte_hash
> 2) move all function bodies from rte_hash_crc.h to separate module,
> leaving prototype definitions there only.
> 
> Everybody's up for the second option? :)
> 
Crud, you're right, I didn't think about the header inclusion issue.  Is it
worth adding the jump to enable the dynamic hash selection?
Neil

> -- 
> Sincerely,
> 
> Yerden Zhumabekov
> State Technical Service
> Astana, KZ
> 
> 
>