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Add AVX-VNNI support for Alder Lake and later.

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In their infinite wisdom, Intel axed AVX512 from Alder Lake
chips (well, not entirely, but we kind of want to use the Gracemont
cores for chess!) but still added VNNI support.
Confusingly enough, this is not the same as VNNI256 support.

This adds a specific AVX-VNNI target that will use this AVX-VNNI
mode, by prefixing the VNNI instructions with the appropriate VEX
prefix, and avoiding AVX512 usage.

This is about 1% faster on P cores:

Result of  20 runs
==================
base (./clang-bmi2   ) =    3306337  +/- 7519
test (./clang-vnni   ) =    3344226  +/- 7388
diff                   =     +37889  +/- 4153

speedup        = +0.0115
P(speedup > 0) =  1.0000

But a nice 3% faster on E cores:

Result of  20 runs
==================
base (./clang-bmi2   ) =    1938054  +/- 28257
test (./clang-vnni   ) =    1994606  +/- 31756
diff                   =     +56552  +/- 3735

speedup        = +0.0292
P(speedup > 0) =  1.0000

This was measured on Clang 13. GCC 11.2 appears to generate
worse code for Alder Lake, though the speedup on the E cores
is similar.

It is possible to run the engine specifically on the P or E using binding,
for example in linux it is possible to use (for an 8 P + 8 E setup like i9-12900K):
taskset -c 0-15 ./stockfish
taskset -c 16-23 ./stockfish
where the first call binds to the P-cores and the second to the E-cores.

closes https://github.com/official-stockfish/Stockfish/pull/3824

No functional change
This commit is contained in:
Gian-Carlo Pascutto
2021-12-01 23:36:14 +01:00
committed by Joost VandeVondele
parent c1f9a359e8
commit c9977aa0a8
2 changed files with 34 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/simd.h
+10 -3
View File
@@ -46,6 +46,13 @@
#define USE_INLINE_ASM
#endif
// Use either the AVX512 or AVX-VNNI version of the VNNI instructions.
#if defined(USE_AVXVNNI)
#define VNNI_PREFIX "%{vex%} "
#else
#define VNNI_PREFIX ""
#endif
namespace Stockfish::Simd {
#if defined (USE_AVX512)
@@ -208,7 +215,7 @@ namespace Stockfish::Simd {
# if defined (USE_VNNI)
# if defined (USE_INLINE_ASM)
asm(
"vpdpbusd %[b], %[a], %[acc]\n\t"
VNNI_PREFIX "vpdpbusd %[b], %[a], %[acc]\n\t"
: [acc]"+v"(acc)
: [a]"v"(a), [b]"vm"(b)
);
@@ -240,8 +247,8 @@ namespace Stockfish::Simd {
# if defined (USE_VNNI)
# if defined (USE_INLINE_ASM)
asm(
"vpdpbusd %[b0], %[a0], %[acc]\n\t"
"vpdpbusd %[b1], %[a1], %[acc]\n\t"
VNNI_PREFIX "vpdpbusd %[b0], %[a0], %[acc]\n\t"
VNNI_PREFIX "vpdpbusd %[b1], %[a1], %[acc]\n\t"
: [acc]"+v"(acc)
: [a0]"v"(a0), [b0]"vm"(b0), [a1]"v"(a1), [b1]"vm"(b1)
);