Re: [PATCH 0/2] rewritten rte_hash_crc() call

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

14.11.2014 6:52, Neil Horman пишет:
> On Thu, Nov 13, 2014 at 06:33:14PM +0100, Thomas Monjalon wrote:
>> Any comment on these patches?
>>
>> 2014-09-03 12:05, Yerden Zhumabekov:
>>> As SSE4.2 provides CRC32 instructions with either 32 and 64 bit operands,
>>> new rte_hash_crc_8byte() call assisted with _mm_crc32_u64 intrinsic may be
>>> useful.
>>>
>>> ... <skipped> ...
>>
> Yeah, sorry I didn't speak up earlier.  I meant to ask if the __mm_crc_u64
> intrinsic will emit software emulated versions of the sse4.2 instruction in the
> event that you build with a config that doesn't enable sse4.2?  If not, then
> NAK, since this will break on the default build.  In that event you'll have to
> modify the new function to do a runtime cpu flags check to either just use the
> instruction inlined with some asm, or emulate it in software.

Hello,

A quick grep on dpdk source shows that rte_hash_crc() is used in
librte_hash in following context:

In rte_hash.c:
/* Hash function used if none is specified */
#ifdef RTE_MACHINE_CPUFLAG_SSE4_2
#include <rte_hash_crc.h>
#define DEFAULT_HASH_FUNC       rte_hash_crc
#else
#include <rte_jhash.h>
#define DEFAULT_HASH_FUNC       rte_jhash
#endif

In rte_fbk_hash.h
#ifdef RTE_MACHINE_CPUFLAG_SSE4_2
#include <rte_hash_crc.h>
/** Default four-byte key hash function if none is specified. */
#define RTE_FBK_HASH_FUNC_DEFAULT·······rte_hash_crc_4byte
#else
#include <rte_jhash.h>
#define RTE_FBK_HASH_FUNC_DEFAULT·······rte_jhash_1word
#endif
#endif


I guess it covers the cpu flags check you're talking about.

-- 
Sincerely,

Yerden Zhumabekov
State Technical Service
Astana, KZ