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

[Yerden Zhumabekov <e_zhumabekov@sts.kz>]

19.11.2014 3:36, Neil Horman пишет:
> On Tue, Nov 18, 2014 at 05:52:27PM +0000, Bruce Richardson wrote:
>> On Tue, Nov 18, 2014 at 12:46:19PM -0500, Neil Horman wrote:
>>> On Tue, Nov 18, 2014 at 11:13:17PM +0600, Yerden Zhumabekov wrote:
>>>> 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
>> Maybe for cases where SSE4.2 is not currently available, i.e. for generic builds.
>> For builds where we have hardware support confirmed at compile time, just use
>> the function from the header file.
>> Does that make sense?
>>
> I'm not certain of that, as I don't think anything can be 'confirmed' at compile
> time.  I.e. just because you have sse42 at compile time doesn't guarantee you
> have it at run time with a DSO.  If you have these as macros, you need to enable
> sse42 whereever you include the file so that the intrinsic works properly.
>
> an alternate option would be to not use the intrinsic, and craft some explicit
> __asm__ statement that executes the right sse42 instructions.  That way the asm
> is directly emitted, without requiring the -msse42 flag at all, and it will just
> work in all the files that call it.

Thanks for the discussion. To summarize it with my suggestions for 'v5':
1) replace intrinsics with asm code and give up including nmmintrin.h;
2) detect arch (EM64T flag) on runtime because crc32 for 64-bit operand
doesn't work on 32-bit x86;
3) separate function prototypes (leaving them in header) and bodies, add
to SRCS in Makefile.

-- 
Sincerely,

Yerden Zhumabekov
State Technical Service
Astana, KZ