[dpdk-dev] [PATCH v3 3/5] hash: add fallback to software CRC32 implementation

[Neil Horman]

On Tue, Nov 18, 2014 at 10:56:24AM +0600, Yerden Zhumabekov wrote:
> Sorry, maybe I made a mistake here.
> 
> Accoring to lib/librte_eal/common/eal_common_cpuflags.c code, it seemed
> to me that constructor attribute is not supported by intel compiler. So
> in that case here I decided to leave the code for autodetection. Am I
> correct?
> 

I don't think thats correct. The Intel Compiler claims support for most GCC
features, except where explicitly stated in the release notes, and I don't find
any documentation clearly excepting the constructor attribute from that list.
That said, since the intel compiler isn't open, I don't have access to it and
cannot confirm either way, though if its the case, the DPDK has a major issue,
as __attribute__((constructor)) is used extensively throughout the code
Neil



> 18.11.2014 9:21, Yerden Zhumabekov пишет:
> > 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.
> >
> > Depending on compiler attributes support, best available algorithm
> > may be detected upon application startup.
> >
> > Signed-off-by: Yerden Zhumabekov <e_zhumabekov at sts.kz>
> > ---
> >  lib/librte_hash/rte_hash_crc.h |   64 ++++++++++++++++++++++++++++++++++++++--
> >  1 file changed, 62 insertions(+), 2 deletions(-)
> >
> > diff --git a/lib/librte_hash/rte_hash_crc.h b/lib/librte_hash/rte_hash_crc.h
> > index 15f687a..c1b75e8 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 +367,44 @@ crc32c_2words(uint64_t data, uint32_t init_val)
> >  	return crc;
> >  }
> >  
> > +enum crc32_alg_t {
> > +	CRC32_SW = 0,
> > +	CRC32_SSE42,
> > +	CRC32_AUTODETECT
> > +};
> > +
> > +static enum crc32_alg_t crc32_alg = CRC32_AUTODETECT;
> > +
> > +/**
> > + * 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 */
> > +#ifndef __INTEL_COMPILER
> > +static inline void __attribute__((constructor))
> > +rte_hash_crc_try_sse42(void)
> > +{
> > +	rte_hash_crc_set_alg(CRC32_SSE42);
> > +}
> > +#endif
> > +
> >  /**
> >   * 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 +416,22 @@ 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 __INTEL_COMPILER
> > +	if (unlikely(crc32_alg == CRC32_AUTODETECT))
> > +		rte_hash_crc_set_alg(CRC32_SSE42);
> > +#endif
> > +#ifdef RTE_MACHINE_CPUFLAG_SSE4_2
> > +	if (likely(crc32_alg == CRC32_SSE42))
> > +		return _mm_crc32_u32(init_val, data);
> > +#endif
> > +
> > +	return crc32c_1word(data, init_val);
> >  }
> >  
> >  /**
> >   * Use single crc32 instruction to perform a hash on a 8 byte value.
> > + * Fall back to software crc32 implementation in case SSE4.2 is
> > + * not supported
> >   *
> >   * @param data
> >   *   Data to perform hash on.
> > @@ -392,7 +443,16 @@ rte_hash_crc_4byte(uint32_t data, uint32_t init_val)
> >  static inline uint32_t
> >  rte_hash_crc_8byte(uint64_t data, uint32_t init_val)
> >  {
> > -	return _mm_crc32_u64(init_val, data);
> > +#ifdef __INTEL_COMPILER
> > +	if (unlikely(crc32_alg == CRC32_AUTODETECT))
> > +		rte_hash_crc_set_alg(CRC32_SSE42);
> > +#endif
> > +#ifdef RTE_MACHINE_CPUFLAG_SSE4_2
> > +	if (likely(crc32_alg == CRC32_SSE42))
> > +		return _mm_crc32_u64(init_val, data);
> > +#endif
> > +
> > +	return crc32c_2words(data, init_val);
> >  }
> >  
> >  /**
> 
> -- 
> Sincerely,
> 
> Yerden Zhumabekov
> State Technical Service
> Astana, KZ
> 
>