Trellis quants: faster CPU prompt processing#482
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May 31, 2025 11:08
For iq4_kt this results in a massive PP improvement from PP512 = ~42 t/s to PP512 = 128 t/s.
iq2_kt: from PP512 = 57.3 t/s to PP512 = 135.0 t/s iq3_kt: from PP512 = 43.8 t/s to PP512 = 131.4 t/s
iq2_kt: PP512 = 79 t/s from 42 t/s iq3_kt: PP512 = 81 t/s from 35 t/s Also, found the reason why the f16 implementation for iq4_kt was not working: it overflows. It works after mltiplying with the row scale before doing the multiply-adds.
iq4_kt: PP512 = 86 t/s from 29 t/s
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* iq2_kt: Metal dequantize * iq2_kt: Metal GEMV Performance is actually quite decent: 52 t/s on my M2-Max for LlaMA-3.1-8B * iq3_kt: Metal dequantize * iq3_kt: Metal GEMV Performance is not as good as iq2_kt: 40 t/s on my M2-Max for LlaMA-3.1-8B. Flipping signs is a costly affair. * iq4_kt: Metal dequantize - getting NaNs * iq4_kt: Metal GEMV - also not working * iq4_kt: Metal still not working * Disable iq4_kt on Metal for now --------- Trellis quants: faster CPU prompt processing (ikawrakow#482) * Experimenting with dequant + f32 GEMM For iq4_kt this results in a massive PP improvement from PP512 = ~42 t/s to PP512 = 128 t/s. * Experimenting with dequant + f32 GEMM iq2_kt: from PP512 = 57.3 t/s to PP512 = 135.0 t/s iq3_kt: from PP512 = 43.8 t/s to PP512 = 131.4 t/s * Experimenting with dequant + f16 GEMM on NEON iq2_kt: PP512 = 79 t/s from 42 t/s iq3_kt: PP512 = 81 t/s from 35 t/s Also, found the reason why the f16 implementation for iq4_kt was not working: it overflows. It works after mltiplying with the row scale before doing the multiply-adds. * Experimenting with dequant + f16 GEMM on NEON iq4_kt: PP512 = 86 t/s from 29 t/s * Minor --------- Minor (~2%) iq2_ks TG performance improvement on CUDA (ikawrakow#468) Direct conversion from fp16 to Q6_0
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The trellis quants
IQ2_KT, IQ3_KT, IQ4_KTare very slow on the CPU. On the main branch using BLAS results in a better prompt processing performance. But BLAS is slower for basically all other data types, so that's not a good idea.This PR improves prompt processing speed of the trellis quants by adding "dequantizing GEMM". Basically, blocks of trelis quantized weights are converted to
fp32(AVX2 )orfp16(ARM) on-the-fly, and then thefp32/fp16GEMM kernels are used to multiply the bock with the entire right matrix. This amortizes the very high dequantization cost much better than the standard kernel templates that allow up to 8 right matrix columns.On my
Zen4/AVX2CPUs this results in a better PP performance than using BLAS (or Intel MKL). On the M2-Max PP performance is about 80% of BLAS (which tells me that myARM_NEONGEMM kernel forfp16is not optimal).TG performance is not affected by the PR and is still very low.
Here is a PP-512 performance comparison between the main branch (without BLAS) and this PR for LlaMA-3.1-8B on a Ryzen-7950X CPU