[FFmpeg-devel] [PATCH 1/2] libavutil/cpu: Add AV_CPU_FLAG_SLOW_GATHER.

Alan Kelly alankelly at google.com
Mon Dec 20 15:56:27 EET 2021


This flag is set on Haswell and earlier and all AMD cpus.
---
 As discussed on IRC last week.
 libavutil/cpu.h     | 57 +++++++++++++++++++++++----------------------
 libavutil/x86/cpu.c | 13 ++++++++++-
 2 files changed, 41 insertions(+), 29 deletions(-)

diff --git a/libavutil/cpu.h b/libavutil/cpu.h
index ae443eccad..4272d11d73 100644
--- a/libavutil/cpu.h
+++ b/libavutil/cpu.h
@@ -26,34 +26,35 @@
 #define AV_CPU_FLAG_FORCE    0x80000000 /* force usage of selected flags (OR) */
 
     /* lower 16 bits - CPU features */
-#define AV_CPU_FLAG_MMX          0x0001 ///< standard MMX
-#define AV_CPU_FLAG_MMXEXT       0x0002 ///< SSE integer functions or AMD MMX ext
-#define AV_CPU_FLAG_MMX2         0x0002 ///< SSE integer functions or AMD MMX ext
-#define AV_CPU_FLAG_3DNOW        0x0004 ///< AMD 3DNOW
-#define AV_CPU_FLAG_SSE          0x0008 ///< SSE functions
-#define AV_CPU_FLAG_SSE2         0x0010 ///< PIV SSE2 functions
-#define AV_CPU_FLAG_SSE2SLOW 0x40000000 ///< SSE2 supported, but usually not faster
-                                        ///< than regular MMX/SSE (e.g. Core1)
-#define AV_CPU_FLAG_3DNOWEXT     0x0020 ///< AMD 3DNowExt
-#define AV_CPU_FLAG_SSE3         0x0040 ///< Prescott SSE3 functions
-#define AV_CPU_FLAG_SSE3SLOW 0x20000000 ///< SSE3 supported, but usually not faster
-                                        ///< than regular MMX/SSE (e.g. Core1)
-#define AV_CPU_FLAG_SSSE3        0x0080 ///< Conroe SSSE3 functions
-#define AV_CPU_FLAG_SSSE3SLOW 0x4000000 ///< SSSE3 supported, but usually not faster
-#define AV_CPU_FLAG_ATOM     0x10000000 ///< Atom processor, some SSSE3 instructions are slower
-#define AV_CPU_FLAG_SSE4         0x0100 ///< Penryn SSE4.1 functions
-#define AV_CPU_FLAG_SSE42        0x0200 ///< Nehalem SSE4.2 functions
-#define AV_CPU_FLAG_AESNI       0x80000 ///< Advanced Encryption Standard functions
-#define AV_CPU_FLAG_AVX          0x4000 ///< AVX functions: requires OS support even if YMM registers aren't used
-#define AV_CPU_FLAG_AVXSLOW   0x8000000 ///< AVX supported, but slow when using YMM registers (e.g. Bulldozer)
-#define AV_CPU_FLAG_XOP          0x0400 ///< Bulldozer XOP functions
-#define AV_CPU_FLAG_FMA4         0x0800 ///< Bulldozer FMA4 functions
-#define AV_CPU_FLAG_CMOV         0x1000 ///< supports cmov instruction
-#define AV_CPU_FLAG_AVX2         0x8000 ///< AVX2 functions: requires OS support even if YMM registers aren't used
-#define AV_CPU_FLAG_FMA3        0x10000 ///< Haswell FMA3 functions
-#define AV_CPU_FLAG_BMI1        0x20000 ///< Bit Manipulation Instruction Set 1
-#define AV_CPU_FLAG_BMI2        0x40000 ///< Bit Manipulation Instruction Set 2
-#define AV_CPU_FLAG_AVX512     0x100000 ///< AVX-512 functions: requires OS support even if YMM/ZMM registers aren't used
+#define AV_CPU_FLAG_MMX             0x0001 ///< standard MMX
+#define AV_CPU_FLAG_MMXEXT          0x0002 ///< SSE integer functions or AMD MMX ext
+#define AV_CPU_FLAG_MMX2            0x0002 ///< SSE integer functions or AMD MMX ext
+#define AV_CPU_FLAG_3DNOW           0x0004 ///< AMD 3DNOW
+#define AV_CPU_FLAG_SSE             0x0008 ///< SSE functions
+#define AV_CPU_FLAG_SSE2            0x0010 ///< PIV SSE2 functions
+#define AV_CPU_FLAG_SSE2SLOW    0x40000000 ///< SSE2 supported, but usually not faster
+                                           ///< than regular MMX/SSE (e.g. Core1)
+#define AV_CPU_FLAG_3DNOWEXT        0x0020 ///< AMD 3DNowExt
+#define AV_CPU_FLAG_SSE3            0x0040 ///< Prescott SSE3 functions
+#define AV_CPU_FLAG_SSE3SLOW    0x20000000 ///< SSE3 supported, but usually not faster
+                                           ///< than regular MMX/SSE (e.g. Core1)
+#define AV_CPU_FLAG_SSSE3           0x0080 ///< Conroe SSSE3 functions
+#define AV_CPU_FLAG_SSSE3SLOW    0x4000000 ///< SSSE3 supported, but usually not faster
+#define AV_CPU_FLAG_ATOM        0x10000000 ///< Atom processor, some SSSE3 instructions are slower
+#define AV_CPU_FLAG_SSE4            0x0100 ///< Penryn SSE4.1 functions
+#define AV_CPU_FLAG_SSE42           0x0200 ///< Nehalem SSE4.2 functions
+#define AV_CPU_FLAG_AESNI          0x80000 ///< Advanced Encryption Standard functions
+#define AV_CPU_FLAG_AVX             0x4000 ///< AVX functions: requires OS support even if YMM registers aren't used
+#define AV_CPU_FLAG_AVXSLOW      0x8000000 ///< AVX supported, but slow when using YMM registers (e.g. Bulldozer)
+#define AV_CPU_FLAG_XOP             0x0400 ///< Bulldozer XOP functions
+#define AV_CPU_FLAG_FMA4            0x0800 ///< Bulldozer FMA4 functions
+#define AV_CPU_FLAG_CMOV            0x1000 ///< supports cmov instruction
+#define AV_CPU_FLAG_AVX2            0x8000 ///< AVX2 functions: requires OS support even if YMM registers aren't used
+#define AV_CPU_FLAG_FMA3           0x10000 ///< Haswell FMA3 functions
+#define AV_CPU_FLAG_BMI1           0x20000 ///< Bit Manipulation Instruction Set 1
+#define AV_CPU_FLAG_BMI2           0x40000 ///< Bit Manipulation Instruction Set 2
+#define AV_CPU_FLAG_AVX512        0x100000 ///< AVX-512 functions: requires OS support even if YMM/ZMM registers aren't used
+#define AV_CPU_FLAG_SLOW_GATHER  0x2000000 ///< CPU has slow gathers.
 
 #define AV_CPU_FLAG_ALTIVEC      0x0001 ///< standard
 #define AV_CPU_FLAG_VSX          0x0002 ///< ISA 2.06
diff --git a/libavutil/x86/cpu.c b/libavutil/x86/cpu.c
index bcd41a50a2..5770ecec72 100644
--- a/libavutil/x86/cpu.c
+++ b/libavutil/x86/cpu.c
@@ -146,8 +146,16 @@ int ff_get_cpu_flags_x86(void)
     if (max_std_level >= 7) {
         cpuid(7, eax, ebx, ecx, edx);
 #if HAVE_AVX2
-        if ((rval & AV_CPU_FLAG_AVX) && (ebx & 0x00000020))
+        if ((rval & AV_CPU_FLAG_AVX) && (ebx & 0x00000020)) {
             rval |= AV_CPU_FLAG_AVX2;
+            cpuid(1, eax, ebx, ecx, std_caps);
+            family = ((eax >> 8) & 0xf) + ((eax >> 20) & 0xff);
+            model  = ((eax >> 4) & 0xf) + ((eax >> 12) & 0xf0);
+            /* Haswell and earlier has slow gather */
+            if(family == 6 && model < 70)
+                rval |= AV_CPU_FLAG_SLOW_GATHER;
+        }
+
 #if HAVE_AVX512 /* F, CD, BW, DQ, VL */
         if ((xcr0_lo & 0xe0) == 0xe0) { /* OPMASK/ZMM state */
             if ((rval & AV_CPU_FLAG_AVX2) && (ebx & 0xd0030000) == 0xd0030000)
@@ -196,6 +204,9 @@ int ff_get_cpu_flags_x86(void)
            used unless explicitly disabled by checking AV_CPU_FLAG_AVXSLOW. */
             if ((family == 0x15 || family == 0x16) && (rval & AV_CPU_FLAG_AVX))
                 rval |= AV_CPU_FLAG_AVXSLOW;
+
+        /* AMD cpus have slow gather */
+            rval |= AV_CPU_FLAG_SLOW_GATHER;
         }
 
         /* XOP and FMA4 use the AVX instruction coding scheme, so they can't be
-- 
2.34.1.173.g76aa8bc2d0-goog



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