[dpdk-dev] [PATCH] build: fix memcpy behaviour regression

[Bruce Richardson <bruce.richardson@intel.com>]

When testing on some x86 platforms, code compiled with meson was observed
running at a different power-license level to that compiled with make. This
is due to the fact that meson auto-detects the instruction sets available
on the system and enabled AVX512 rte_memcpy when AVX512 was available,
while on make, a build time AVX-512 flag needed to be explicitly set to
enable that AVX512 rte_memcpy code path.

In the absense of runtime path selection for rte_memcpy - which is
complicated by it being a static inline function in a header file - we can
fix this behaviour regression by similarly having a build-time option which
must be set to enable the AVX-512 memcpy path.

Fixes: a25a650be5f0 ("build: add infrastructure for meson and ninja builds")
Fixes: 3e1bb55fd6ef ("build/x86: add SSE flags")

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>

---
NOTE: This patch is not suitable for backporting, as it will break the
build support for make builds without addition makefile changes.
---
 lib/librte_eal/include/generic/rte_memcpy.h | 4 ++++
 lib/librte_eal/x86/include/rte_memcpy.h     | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/lib/librte_eal/include/generic/rte_memcpy.h b/lib/librte_eal/include/generic/rte_memcpy.h
index 701e550c3..e7f0f8eaa 100644
--- a/lib/librte_eal/include/generic/rte_memcpy.h
+++ b/lib/librte_eal/include/generic/rte_memcpy.h
@@ -95,6 +95,10 @@ rte_mov256(uint8_t *dst, const uint8_t *src);
  * @note This is implemented as a macro, so it's address should not be taken
  * and care is needed as parameter expressions may be evaluated multiple times.
  *
+ * @note For x86 platforms to enable the AVX-512 memcpy implementation, set
+ * -DRTE_MEMCPY_AVX512 macro in CFLAGS, or define the RTE_MEMCPY_AVX512 macro
+ * explicitly in the source file before including the rte_memcpy header file.
+ *
  * @param dst
  *   Pointer to the destination of the data.
  * @param src
diff --git a/lib/librte_eal/x86/include/rte_memcpy.h b/lib/librte_eal/x86/include/rte_memcpy.h
index 008a3de67..79f381dd9 100644
--- a/lib/librte_eal/x86/include/rte_memcpy.h
+++ b/lib/librte_eal/x86/include/rte_memcpy.h
@@ -45,7 +45,7 @@ extern "C" {
 static __rte_always_inline void *
 rte_memcpy(void *dst, const void *src, size_t n);
 
-#ifdef __AVX512F__
+#if defined __AVX512F__ && defined RTE_MEMCPY_AVX512
 
 #define ALIGNMENT_MASK 0x3F
 
-- 
2.25.1