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

[Yerden Zhumabekov]

18.11.2014 20:41, Neil Horman пишет:
> On Tue, Nov 18, 2014 at 08:03:40PM +0600, Yerden Zhumabekov wrote:
>> Initially, SSE4.2 support is detected via CPUID instruction.
>>
>> Added rte_hash_crc_set_alg() function to detect and set CRC32
>> implementation if necessary. SSE4.2 is allowed by default. If it's
>> not available, fall back to sw implementation.
>>
>> Best available algorithm is detected upon application startup
>> through the constructor function rte_hash_crc_try_sse442().
>>
>> Signed-off-by: Yerden Zhumabekov <e_zhumabekov at sts.kz>
>> ---
>>  lib/librte_hash/rte_hash_crc.h |   53 ++++++++++++++++++++++++++++++++++++++--
>>  1 file changed, 51 insertions(+), 2 deletions(-)
>>
>> diff --git a/lib/librte_hash/rte_hash_crc.h b/lib/librte_hash/rte_hash_crc.h
>> index 15f687a..332ed99 100644
>> --- a/lib/librte_hash/rte_hash_crc.h
>> +++ b/lib/librte_hash/rte_hash_crc.h
>> @@ -45,7 +45,11 @@ extern "C" {
>>  #endif
>>  
>>  #include <stdint.h>
>> +#ifdef RTE_MACHINE_CPUFLAG_SSE4_2
>>  #include <nmmintrin.h>
>> +#endif
>> +#include <rte_cpuflags.h>
>> +#include <rte_branch_prediction.h>
>>  
>>  /* Lookup tables for software implementation of CRC32C */
>>  static uint32_t crc32c_tables[8][256] = {{
>> @@ -363,8 +367,41 @@ crc32c_2words(uint64_t data, uint32_t init_val)
>>  	return crc;
>>  }
>>  
>> +enum crc32_alg_t {
>> +	CRC32_SW = 0,
>> +	CRC32_SSE42
>> +};
>> +
>> +static enum crc32_alg_t crc32_alg;
>> +
>> +/**
>> + * Allow or disallow use of SSE4.2 instrinsics for CRC32 hash
>> + * calculation.
>> + *
>> + * @param flag
>> + *   unsigned integer flag
>> + *   - (CRC32_SW) Don't use SSE4.2 intrinsics
>> + *   - (CRC32_SSE42) Use SSE4.2 intrinsics if available, set by default
>> + */
>> +static inline void
>> +rte_hash_crc_set_alg(enum crc32_alg_t alg)
>> +{
>> +	int sse42_supp = rte_cpu_get_flag_enabled(RTE_CPUFLAG_SSE4_2);
>> +	enum crc32_alg_t alg_supp = sse42_supp ? CRC32_SSE42 : CRC32_SW;
>> +	crc32_alg = (alg == CRC32_SSE42) ? alg_supp : CRC32_SW;
>> +}
>> +
>> +/* Best available algorithm is detected via CPUID instruction */
>> +static inline void __attribute__((constructor))
>> +rte_hash_crc_try_sse42(void)
>> +{
>> +	rte_hash_crc_set_alg(CRC32_SSE42);
>> +}
>> +
>>  /**
>>   * 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.

-- 
Sincerely,

Yerden Zhumabekov
State Technical Service
Astana, KZ