Re: [PATCH v4 3/5] hash: add fallback to software CRC32 implementation

[Yerden Zhumabekov <e_zhumabekov-8EHiFRVJVgQ@public.gmane.org>]

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? :)

-- 
Sincerely,

Yerden Zhumabekov
State Technical Service
Astana, KZ