PING for review. Regardless if you - for good and valid reasons - generally prefer memcpy() over rte_memcpy(), rte_memcpy() is not deprecated or being phased out, so improvements should be allowed.
> From: Morten Brørup [mailto:[email protected]] > Sent: Monday, 1 December 2025 16.55 > > eal/x86: optimize memcpy of small sizes > > The implementation for copying up to 64 bytes does not depend on > address > alignment with the size of the CPU's vector registers, so the code > handling this was moved from the various implementations to the common > function. > > Furthermore, the function for copying less than 16 bytes was replaced > with > a smarter implementation using fewer branches and potentially fewer > load/store operations. > This function was also extended to handle copying of up to 16 bytes, > instead of up to 15 bytes. This small extension reduces the code path > for > copying two pointers. > > These changes provide two benefits: > 1. The memory footprint of the copy function is reduced. > Previously there were two instances of the compiled code to copy up to > 64 > bytes, one in the "aligned" code path, and one in the "generic" code > path. > Now there is only one instance, in the "common" code path. > 2. The performance for copying up to 64 bytes is improved. > The memcpy performance test shows cache-to-cache copying of up to 32 > bytes > now typically only takes 2 cycles (4 cycles for 64 bytes) versus > ca. 6.5 cycles before this patch. > > And finally, the missing implementation of rte_mov48() was added. > > Signed-off-by: Morten Brørup <[email protected]> > --- > v5: > * Reverted v4: Replace SSE2 _mm_loadu_si128() with SSE3 > _mm_lddqu_si128(). > It was slower. > * Improved some comments. (Konstantin Ananyev) > * Moved the size range 17..32 inside the size <= 64 branch, so when > building for SSE, the generated code can start copying the first > 16 bytes before comparing if the size is greater than 32 or not. > * Just require RTE_MEMCPY_AVX for using rte_mov32() in > rte_mov33_to_64(). > v4: > * Replace SSE2 _mm_loadu_si128() with SSE3 _mm_lddqu_si128(). > v3: > * Fixed typo in comment. > v2: > * Updated patch title to reflect that the performance is improved. > * Use the design pattern of two overlapping stores for small copies > too. > * Expanded first branch from size < 16 to size <= 16. > * Handle more build time constant copy sizes. > --- > lib/eal/x86/include/rte_memcpy.h | 346 +++++++++++++++++-------------- > 1 file changed, 186 insertions(+), 160 deletions(-) > > diff --git a/lib/eal/x86/include/rte_memcpy.h > b/lib/eal/x86/include/rte_memcpy.h > index 46d34b8081..04d1a474d1 100644 > --- a/lib/eal/x86/include/rte_memcpy.h > +++ b/lib/eal/x86/include/rte_memcpy.h > @@ -55,52 +55,6 @@ extern "C" { > static __rte_always_inline void * > rte_memcpy(void *dst, const void *src, size_t n); > > -/** > - * Copy bytes from one location to another, > - * locations should not overlap. > - * Use with n <= 15. > - */ > -static __rte_always_inline void * > -rte_mov15_or_less(void *dst, const void *src, size_t n) > -{ > - /** > - * Use the following structs to avoid violating C standard > - * alignment requirements and to avoid strict aliasing bugs > - */ > - struct __rte_packed_begin rte_uint64_alias { > - uint64_t val; > - } __rte_packed_end __rte_may_alias; > - struct __rte_packed_begin rte_uint32_alias { > - uint32_t val; > - } __rte_packed_end __rte_may_alias; > - struct __rte_packed_begin rte_uint16_alias { > - uint16_t val; > - } __rte_packed_end __rte_may_alias; > - > - void *ret = dst; > - if (n & 8) { > - ((struct rte_uint64_alias *)dst)->val = > - ((const struct rte_uint64_alias *)src)->val; > - src = (const uint64_t *)src + 1; > - dst = (uint64_t *)dst + 1; > - } > - if (n & 4) { > - ((struct rte_uint32_alias *)dst)->val = > - ((const struct rte_uint32_alias *)src)->val; > - src = (const uint32_t *)src + 1; > - dst = (uint32_t *)dst + 1; > - } > - if (n & 2) { > - ((struct rte_uint16_alias *)dst)->val = > - ((const struct rte_uint16_alias *)src)->val; > - src = (const uint16_t *)src + 1; > - dst = (uint16_t *)dst + 1; > - } > - if (n & 1) > - *(uint8_t *)dst = *(const uint8_t *)src; > - return ret; > -} > - > /** > * Copy 16 bytes from one location to another, > * locations should not overlap. > @@ -132,6 +86,23 @@ rte_mov32(uint8_t *dst, const uint8_t *src) > #endif > } > > +/** > + * Copy 48 bytes from one location to another, > + * locations should not overlap. > + */ > +static __rte_always_inline void > +rte_mov48(uint8_t *dst, const uint8_t *src) > +{ > +#if defined RTE_MEMCPY_AVX > + rte_mov32((uint8_t *)dst, (const uint8_t *)src); > + rte_mov32((uint8_t *)dst - 32 + 48, (const uint8_t *)src - 32 + > 48); > +#else /* SSE implementation */ > + rte_mov16((uint8_t *)dst + 0 * 16, (const uint8_t *)src + 0 * > 16); > + rte_mov16((uint8_t *)dst + 1 * 16, (const uint8_t *)src + 1 * > 16); > + rte_mov16((uint8_t *)dst + 2 * 16, (const uint8_t *)src + 2 * > 16); > +#endif > +} > + > /** > * Copy 64 bytes from one location to another, > * locations should not overlap. > @@ -172,6 +143,137 @@ rte_mov256(uint8_t *dst, const uint8_t *src) > rte_mov128(dst + 1 * 128, src + 1 * 128); > } > > +/** > + * Copy bytes from one location to another, > + * locations should not overlap. > + * Use with n <= 16. > + * > + * Note: Copying uninitialized memory is perfectly acceptable. > + * Using e.g. memcpy(dst, src, 8) instead of > + * *(unaligned_uint64_t*) = *(const unaligned_uint64_t *)src > + * avoids compiler warnings about source data may be uninitialized > + * [-Wmaybe-uninitialized]. > + */ > +static __rte_always_inline void * > +rte_mov16_or_less(void *dst, const void *src, size_t n) > +{ > + /* Faster way when size is known at build time. */ > + if (__rte_constant(n)) { > + if (n == 2) > + return memcpy(dst, src, 2); > + if (n == 4) > + return memcpy(dst, src, 4); > + if (n == 6) /* 4 + 2 */ > + return memcpy(dst, src, 6); > + if (n == 8) > + return memcpy(dst, src, 8); > + if (n == 10) /* 8 + 2 */ > + return memcpy(dst, src, 10); > + if (n == 12) /* 8 + 4 */ > + return memcpy(dst, src, 12); > + if (n == 16) { > + rte_mov16((uint8_t *)dst, (const uint8_t *)src); > + return dst; > + } > + } > + > + /* > + * Note: Using "n & X" generates 3-byte "test" instructions, > + * instead of "n >= X", which would generate 4-byte "cmp" > instructions. > + */ > + if (n & 0x18) { /* n >= 8, including n == 0x10, hence n & 0x18. > */ > + /* Copy 8 ~ 16 bytes. */ > + memcpy(dst, src, 8); > + memcpy((uint8_t *)dst - 8 + n, (const uint8_t *)src - 8 + > n, 8); > + } else if (n & 0x4) { > + /* Copy 4 ~ 7 bytes. */ > + memcpy(dst, src, 4); > + memcpy((uint8_t *)dst - 4 + n, (const uint8_t *)src - 4 + > n, 4); > + } else if (n & 0x2) { > + /* Copy 2 ~ 3 bytes. */ > + memcpy(dst, src, 2); > + memcpy((uint8_t *)dst - 2 + n, (const uint8_t *)src - 2 + > n, 2); > + } else if (n & 0x1) { > + /* Copy 1 byte. */ > + memcpy(dst, src, 1); > + } > + return dst; > +} > + > +/** > + * Copy bytes from one location to another, > + * locations should not overlap. > + * Use with 17 (or 16) < n <= 32. > + */ > +static __rte_always_inline void * > +rte_mov17_to_32(void *dst, const void *src, size_t n) > +{ > + /* Faster way when size is known at build time. */ > + if (__rte_constant(n)) { > + if (n == 16) { > + rte_mov16((uint8_t *)dst, (const uint8_t *)src); > + return dst; > + } > + if (n == 18) /* 16 + 2 */ > + return memcpy(dst, src, 18); > + if (n == 20) /* 16 + 4 */ > + return memcpy(dst, src, 20); > + if (n == 24) /* 16 + 8 */ > + return memcpy(dst, src, 24); > + if (n == 32) { > + rte_mov32((uint8_t *)dst, (const uint8_t *)src); > + return dst; > + } > + } > + > + /* Copy 17 (or 16) ~ 32 bytes. */ > + rte_mov16((uint8_t *)dst, (const uint8_t *)src); > + rte_mov16((uint8_t *)dst - 16 + n, (const uint8_t *)src - 16 + > n); > + return dst; > +} > + > +/** > + * Copy bytes from one location to another, > + * locations should not overlap. > + * Use with 33 (or 32) < n <= 64. > + */ > +static __rte_always_inline void * > +rte_mov33_to_64(void *dst, const void *src, size_t n) > +{ > + /* Faster way when size is known at build time. */ > + if (__rte_constant(n)) { > + if (n == 32) { > + rte_mov32((uint8_t *)dst, (const uint8_t *)src); > + return dst; > + } > + if (n == 36) /* 32 + 4 */ > + return memcpy(dst, src, 36); > + if (n == 40) /* 32 + 8 */ > + return memcpy(dst, src, 40); > + if (n == 48) { > + rte_mov48((uint8_t *)dst, (const uint8_t *)src); > + return dst; > + } > + if (n == 64) { > + rte_mov64((uint8_t *)dst, (const uint8_t *)src); > + return dst; > + } > + } > + > + /* Copy 33 (or 32) ~ 64 bytes. */ > +#if defined RTE_MEMCPY_AVX > + rte_mov32((uint8_t *)dst, (const uint8_t *)src); > + rte_mov32((uint8_t *)dst - 32 + n, (const uint8_t *)src - 32 + > n); > +#else /* SSE implementation */ > + rte_mov16((uint8_t *)dst + 0 * 16, (const uint8_t *)src + 0 * > 16); > + rte_mov16((uint8_t *)dst + 1 * 16, (const uint8_t *)src + 1 * > 16); > + if (n > 48) > + rte_mov16((uint8_t *)dst + 2 * 16, (const uint8_t *)src + 2 > * 16); > + rte_mov16((uint8_t *)dst - 16 + n, (const uint8_t *)src - 16 + > n); > +#endif > + return dst; > +} > + > #if defined __AVX512F__ && defined RTE_MEMCPY_AVX512 > > /** > @@ -232,45 +334,21 @@ rte_mov512blocks(uint8_t *dst, const uint8_t > *src, size_t n) > } > } > > +/** > + * Copy bytes from one location to another, > + * locations should not overlap. > + * Use with n > 64. > + */ > static __rte_always_inline void * > -rte_memcpy_generic(void *dst, const void *src, size_t n) > +rte_memcpy_generic_more_than_64(void *dst, const void *src, size_t n) > { > void *ret = dst; > size_t dstofss; > size_t bits; > > - /** > - * Copy less than 16 bytes > - */ > - if (n < 16) { > - return rte_mov15_or_less(dst, src, n); > - } > - > /** > * Fast way when copy size doesn't exceed 512 bytes > */ > - if (__rte_constant(n) && n == 32) { > - rte_mov32((uint8_t *)dst, (const uint8_t *)src); > - return ret; > - } > - if (n <= 32) { > - rte_mov16((uint8_t *)dst, (const uint8_t *)src); > - if (__rte_constant(n) && n == 16) > - return ret; /* avoid (harmless) duplicate copy */ > - rte_mov16((uint8_t *)dst - 16 + n, > - (const uint8_t *)src - 16 + n); > - return ret; > - } > - if (__rte_constant(n) && n == 64) { > - rte_mov64((uint8_t *)dst, (const uint8_t *)src); > - return ret; > - } > - if (n <= 64) { > - rte_mov32((uint8_t *)dst, (const uint8_t *)src); > - rte_mov32((uint8_t *)dst - 32 + n, > - (const uint8_t *)src - 32 + n); > - return ret; > - } > if (n <= 512) { > if (n >= 256) { > n -= 256; > @@ -381,41 +459,21 @@ rte_mov128blocks(uint8_t *dst, const uint8_t > *src, size_t n) > } > } > > +/** > + * Copy bytes from one location to another, > + * locations should not overlap. > + * Use with n > 64. > + */ > static __rte_always_inline void * > -rte_memcpy_generic(void *dst, const void *src, size_t n) > +rte_memcpy_generic_more_than_64(void *dst, const void *src, size_t n) > { > void *ret = dst; > size_t dstofss; > size_t bits; > > - /** > - * Copy less than 16 bytes > - */ > - if (n < 16) { > - return rte_mov15_or_less(dst, src, n); > - } > - > /** > * Fast way when copy size doesn't exceed 256 bytes > */ > - if (__rte_constant(n) && n == 32) { > - rte_mov32((uint8_t *)dst, (const uint8_t *)src); > - return ret; > - } > - if (n <= 32) { > - rte_mov16((uint8_t *)dst, (const uint8_t *)src); > - if (__rte_constant(n) && n == 16) > - return ret; /* avoid (harmless) duplicate copy */ > - rte_mov16((uint8_t *)dst - 16 + n, > - (const uint8_t *)src - 16 + n); > - return ret; > - } > - if (n <= 64) { > - rte_mov32((uint8_t *)dst, (const uint8_t *)src); > - rte_mov32((uint8_t *)dst - 32 + n, > - (const uint8_t *)src - 32 + n); > - return ret; > - } > if (n <= 256) { > if (n >= 128) { > n -= 128; > @@ -573,38 +631,22 @@ rte_memcpy_generic(void *dst, const void *src, > size_t n) > } > \ > } > > +/** > + * Copy bytes from one location to another, > + * locations should not overlap. > + * Use with n > 64. > + */ > static __rte_always_inline void * > -rte_memcpy_generic(void *dst, const void *src, size_t n) > +rte_memcpy_generic_more_than_64(void *dst, const void *src, size_t n) > { > __m128i xmm0, xmm1, xmm2, xmm3, xmm4, xmm5, xmm6, xmm7, xmm8; > void *ret = dst; > size_t dstofss; > size_t srcofs; > > - /** > - * Copy less than 16 bytes > - */ > - if (n < 16) { > - return rte_mov15_or_less(dst, src, n); > - } > - > /** > * Fast way when copy size doesn't exceed 512 bytes > */ > - if (n <= 32) { > - rte_mov16((uint8_t *)dst, (const uint8_t *)src); > - if (__rte_constant(n) && n == 16) > - return ret; /* avoid (harmless) duplicate copy */ > - rte_mov16((uint8_t *)dst - 16 + n, (const uint8_t *)src - > 16 + n); > - return ret; > - } > - if (n <= 64) { > - rte_mov32((uint8_t *)dst, (const uint8_t *)src); > - if (n > 48) > - rte_mov16((uint8_t *)dst + 32, (const uint8_t *)src + > 32); > - rte_mov16((uint8_t *)dst - 16 + n, (const uint8_t *)src - > 16 + n); > - return ret; > - } > if (n <= 128) { > goto COPY_BLOCK_128_BACK15; > } > @@ -696,44 +738,16 @@ rte_memcpy_generic(void *dst, const void *src, > size_t n) > > #endif /* __AVX512F__ */ > > +/** > + * Copy bytes from one vector register size aligned location to > another, > + * locations should not overlap. > + * Use with n > 64. > + */ > static __rte_always_inline void * > -rte_memcpy_aligned(void *dst, const void *src, size_t n) > +rte_memcpy_aligned_more_than_64(void *dst, const void *src, size_t n) > { > void *ret = dst; > > - /* Copy size < 16 bytes */ > - if (n < 16) { > - return rte_mov15_or_less(dst, src, n); > - } > - > - /* Copy 16 <= size <= 32 bytes */ > - if (__rte_constant(n) && n == 32) { > - rte_mov32((uint8_t *)dst, (const uint8_t *)src); > - return ret; > - } > - if (n <= 32) { > - rte_mov16((uint8_t *)dst, (const uint8_t *)src); > - if (__rte_constant(n) && n == 16) > - return ret; /* avoid (harmless) duplicate copy */ > - rte_mov16((uint8_t *)dst - 16 + n, > - (const uint8_t *)src - 16 + n); > - > - return ret; > - } > - > - /* Copy 32 < size <= 64 bytes */ > - if (__rte_constant(n) && n == 64) { > - rte_mov64((uint8_t *)dst, (const uint8_t *)src); > - return ret; > - } > - if (n <= 64) { > - rte_mov32((uint8_t *)dst, (const uint8_t *)src); > - rte_mov32((uint8_t *)dst - 32 + n, > - (const uint8_t *)src - 32 + n); > - > - return ret; > - } > - > /* Copy 64 bytes blocks */ > for (; n > 64; n -= 64) { > rte_mov64((uint8_t *)dst, (const uint8_t *)src); > @@ -751,10 +765,22 @@ rte_memcpy_aligned(void *dst, const void *src, > size_t n) > static __rte_always_inline void * > rte_memcpy(void *dst, const void *src, size_t n) > { > + /* Common implementation for size <= 64 bytes. */ > + if (n <= 16) > + return rte_mov16_or_less(dst, src, n); > + if (n <= 64) { > + /* Copy 17 ~ 64 bytes using vector instructions. */ > + if (n <= 32) > + return rte_mov17_to_32(dst, src, n); > + else > + return rte_mov33_to_64(dst, src, n); > + } > + > + /* Implementation for size > 64 bytes depends on alignment with > vector register size. */ > if (!(((uintptr_t)dst | (uintptr_t)src) & ALIGNMENT_MASK)) > - return rte_memcpy_aligned(dst, src, n); > + return rte_memcpy_aligned_more_than_64(dst, src, n); > else > - return rte_memcpy_generic(dst, src, n); > + return rte_memcpy_generic_more_than_64(dst, src, n); > } > > #undef ALIGNMENT_MASK > -- > 2.43.0
