Re: [PATCH v5 4/7] hash: add rte_hash_crc_8byte function

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

21.11.2014 17:22, Neil Horman пишет:
> On Thu, Nov 20, 2014 at 11:16:34AM +0600, Yerden Zhumabekov wrote:
>> SSE4.2 provides CRC32 intrinsic with 8-byte operand.
>>
>> Signed-off-by: Yerden Zhumabekov <e_zhumabekov-8EHiFRVJVgQ@public.gmane.org>
>> ---
>>  lib/librte_hash/rte_hash_crc.h |   16 ++++++++++++++++
>>  1 file changed, 16 insertions(+)
>>
>> diff --git a/lib/librte_hash/rte_hash_crc.h b/lib/librte_hash/rte_hash_crc.h
>> index cd28833..2c8ec99 100644
>> --- a/lib/librte_hash/rte_hash_crc.h
>> +++ b/lib/librte_hash/rte_hash_crc.h
>> @@ -413,6 +413,22 @@ rte_hash_crc_4byte(uint32_t data, uint32_t init_val)
>>  }
>>  
>>  /**
>> + * Use single crc32 instruction to perform a hash on a 8 byte value.
>> + *
>> + * @param data
>> + *   Data to perform hash on.
>> + * @param init_val
>> + *   Value to initialise hash generator.
>> + * @return
>> + *   32bit calculated hash value.
>> + */
>> +static inline uint32_t
>> +rte_hash_crc_8byte(uint64_t data, uint32_t init_val)
>> +{
>> +	return crc32c_sse42_u64(data, init_val);
>> +}
>> +
>> +/**
>>   * Use crc32 instruction to perform a hash.
>>   *
>>   * @param data
>> -- 
>> 1.7.9.5
>>
>>
> I'm sorry, it may be early here, so I may be missing something. The assembly
> implementations look great, but if a user calls rte_hash_crc_8byte on a system
> that doesn't support ss342, how do they wind up getting into the software crc
> implementation given what you have above?
> Neil

After applying patch 4 out of 7 - there's no fall back.  Fall back to SW
crc32 algorithm is in patch 5/7.

Moreover, after patch 5/7  there's a detection if the platform supports
64-bit, otherwise 64-bit operand support is mimicked using two 32-bit
function calls.

-- 
Sincerely,

Yerden Zhumabekov
State Technical Service
Astana, KZ