On Tue, Nov 18, 2014 at 09:06:35PM +0600, Yerden Zhumabekov wrote:
>
> 18.11.2014 20:41, Neil Horman ?????:
> > 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.
>
You need to edit the makefile so that the compiler gets passed the option
-msse42. That way it will know to emit sse42 instructions. It will also allow
you to remove the ifdef from the include file
Neil
> --
> Sincerely,
>
> Yerden Zhumabekov
> State Technical Service
> Astana, KZ
>
>
>
