[dpdk-dev] [PATCH v5 0/7] rte_hash_crc reworked to be platform-independent

Yerden Zhumabekov e_zhumabekov at sts.kz
Fri Nov 28 04:28:49 CET 2014

28.11.2014 3:04, Thomas Monjalon пишет:
> 2014-11-20 11:15, Yerden Zhumabekov:
>> These patches bring a fallback mechanism to ensure that CRC32 hash is calculated regardless of hardware support from CPU (i.e. SSE4.2 intrinsics).
>> Performance is also improved by slicing data in 8 bytes.
>> Patches were tested on machines either with and without SSE4.2 support.
>> Software implementation seems to be about 4-5 times slower than SSE4.2-enabled one. Of course, they return identical results.
>> Summary of changes:
>> * added CRC32 software implementation, which is used as a fallback in case SSE4.2 is not available, or if SSE4.2 is intentionally disabled.
>> * added rte_hash_crc_set_alg() function to control availability of SSE4.2.
>> * added rte_hash_crc_8byte() function to calculate CRC32 on 8-byte operand.
>> * reworked rte_hash_crc() function which leverages both versions of CRC32 hash calculation functions with 4 and 8-byte operands.
>> * removed compile-time checks from test_hash_perf and test_hash.
>> * setting default algorithm implementation as a constructor while application startup.
>> * SSE4.2 intrinsics are implemented through inline assembly code.
>> * added additional run-time check for 64-bit support.
> So you don't want to use the target attribute as suggested by Konstantin?
> Why the discussion ended without any acknowledgement?

I decided to emit SSE4.2 instruction right from the code, because:
* it is supported by gcc 4.3;
* use of target attribute (in a way suggested by Konstantin) presumably
still requires us to use #ifdef which we want to avoid.

Actually then, I didn't investigate it further. I'm quite happy with
last revision, but I'm open for ideas and discussion.
I made new patch series with solely change of crc32c tables declaration
using 'const' just as Stephen suggested, and I may post it. But I'd like
to see a confirmation for what I've done so far.


Yerden Zhumabekov
State Technical Service
Astana, KZ

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