The SiFive U74 (RV64GC; e.g. StarFive JH7110 / VisionFive 2) is a scalar,
in-order core with no RVV, so today it falls back to RISCV64_GENERIC whose
S/D GEMM uses the generic 2x2 C micro-kernel.
Per the U74 Core Complex Manual (Table 169) fmadd.d has a 7-cycle latency
at repeat rate 1 (fully pipelined). A 2x2 tile exposes only 4 independent
accumulator chains -- fewer than the FMA latency -- so the FP pipe stalls
on the accumulator dependency, and the 1:1 load:FMA ratio saturates the
single load/store pipe ("only one outstanding line fill", manual 8.2).
This adds a portable 4x4 GEMM micro-kernel and a dedicated U74 target:
- kernel/generic/gemmkernel_4x4.c: 16-accumulator 4x4 register tile. 16
independent chains exceed the 7-cycle latency, and the load:FMA ratio
drops to 1:2. 16 acc + 4 A + 4 B fit RV64G's 32 FP registers without
spilling. Full 4/2/1 edge handling in both M and N.
- U74 target wiring: getarch.c (FORCE_U74, 32 KiB/64 B L1D, 2 MiB L2),
param.h (S/D UNROLL 4/4; complex stays 2/2), kernel/riscv64/KERNEL.U74
(S/D GEMM -> gemmkernel_4x4 + gemm_[nt]copy_4; S/D TRMM -> existing
trmmkernel_4x4), Makefile.prebuild + Makefile.riscv64 (-mtune=sifive-u74),
TargetList.txt, cpuid_riscv64.c.
The 4x4 kernel was verified numerically against a naive reference GEMM,
driven through the real gemm_tcopy_4 / gemm_ncopy_4 packing routines,
across 27,436 M/N/K x alpha combinations covering every 4/2/1 tail case:
worst absolute error 0.
Build with: make TARGET=U74
This accelerates SBGEMM/BGEMM by extending the existing 8x4 kernel to 8x8 (unrolling N by 8)
Not sure if it's a good idea to delete the previous 8x4 kernel?
Here are the speedups on single core Neoverse-V2 (SVE128) compared to prev state:
Per-shape speedup
M=N=K=64: SBGEMM 1.164x (16.42%), BGEMM 1.133x (13.30%)
M=N=K=128: SBGEMM 1.220x (22.02%), BGEMM 1.186x (18.56%)
M=N=K=256: SBGEMM 1.241x (24.08%), BGEMM 1.235x (23.54%)
M=N=K=512: SBGEMM 1.240x (23.95%), BGEMM 1.227x (22.75%)
M=N=K=1024: SBGEMM 1.251x (25.11%), BGEMM 1.232x (23.23%)
M=N=K=2048: SBGEMM 1.235x (23.47%), BGEMM 1.246x (24.64%)
Signed-off-by: Fadi Arafeh <fadi.arafeh@arm.com>
Added HFLOAT16 support for RISCV64
Added shgemm_kernel_8x8 for RISCV64_ZVL128B and shgemm_kernel_16x8 for RISCV64_ZVL256B based on HFLOAT16
The instruction sets used are ZVFH and ZFH, which need to be supported by RVV1.0
Related to issue #5279
Co-authored-by Linjin Li <linjin_li@163.com>
hmeiland