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perf(matmul): NEON fused dot for Q4_K and Q2_K
Q4_K: scalar → NEON (4-way FMA, 2-way parallel sum_x/dot accumulation) Phi-3.5 Q4_K_M: 1.7 → 3.2 tok/s (1.9x) Llama 3.1 8B Q4_K_M: 0.6 → 1.2 tok/s (2.0x) Q2_K: add fused dot (previously fell through to dequant-then-dot generic path) No measurable speedup (~neutral). Kept for future optimization and to avoid allocating a tmp buffer on each matmul call. Both implementations maintain identical numerical output: - 7/7 model regression tests pass - 35/35 unit tests pass Llama 3.1 8B Q4_K_M vs llama.cpp (100 tokens, 4 threads, no Metal): - Before this session: 0.6 tok/s (llama.cpp ~2.5) = 24% - After (this + Q8_0 auto-quant): 1.2 tok/s = 48% Still lots of headroom — Q3_K NEON and Q2_K further tuning are next targets. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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‎src/engine/tq_gguf_quants.c‎

Lines changed: 163 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -1815,6 +1815,105 @@ static float fused_dot_iq3_xxs(const void* row, const float* x, int n) {
18151815
* First 32 elements: d1 * (q[l] & 0xF) - m1 (low nibble, scale pair[0])
18161816
* Next 32 elements: d2 * (q[l] >> 4) - m2 (high nibble, scale pair[1])
18171817
*/
1818+
/* Fused Q2_K dot product: 84 bytes per 256 elements.
1819+
* 2-bit values packed 4-per-byte in qs[64]. scales[16] holds:
1820+
* low 4 bits = sub-block scale (× d)
1821+
* high 4 bits = sub-block min (× dmin)
1822+
* 16 sub-blocks of 16 elements each. Formula per sub-block:
1823+
* sum += dl * dot(q2_values, x) - ml * sum(x)
1824+
* where q2_values are unsigned 2-bit values in [0, 3]. */
1825+
static float fused_dot_q2_k(const void* row, const float* x, int n) {
1826+
const int nb = n / 256;
1827+
const block_q2_K* blk = (const block_q2_K*)row;
1828+
float sum = 0.0f;
1829+
1830+
for (int b = 0; b < nb; b++) {
1831+
const float d = fp16_to_fp32(blk[b].d);
1832+
const float dmin = fp16_to_fp32(blk[b].dmin);
1833+
const uint8_t* q = blk[b].qs;
1834+
const float* xp = x + b * 256;
1835+
1836+
int is = 0;
1837+
/* 2 halves, 4 shifts per half, 2 sub-blocks per shift */
1838+
for (int half = 0; half < 2; half++) {
1839+
int shift = 0;
1840+
for (int j = 0; j < 4; ++j) {
1841+
/* Sub-block 0: q[0..15] >> shift & 3 */
1842+
uint8_t sc0 = blk[b].scales[is++];
1843+
float dl0 = d * (sc0 & 0x0F);
1844+
float ml0 = dmin * (sc0 >> 4);
1845+
1846+
/* Sub-block 1: q[16..31] >> shift & 3 */
1847+
uint8_t sc1 = blk[b].scales[is++];
1848+
float dl1 = d * (sc1 & 0x0F);
1849+
float ml1 = dmin * (sc1 >> 4);
1850+
1851+
#if TQ_HAS_NEON
1852+
/* Load 16 packed bytes, extract 2-bit values, dot with x.
1853+
* Mask is uint8x16_t of 0x03; shift applied via vshrq_n_u8. */
1854+
uint8x16_t qv0 = vld1q_u8(q); /* sub-block 0 bytes */
1855+
uint8x16_t qv1 = vld1q_u8(q + 16); /* sub-block 1 bytes */
1856+
uint8x16_t m03 = vdupq_n_u8(0x03);
1857+
uint8x16_t v0, v1;
1858+
switch (shift) {
1859+
case 0: v0 = vandq_u8(qv0, m03); v1 = vandq_u8(qv1, m03); break;
1860+
case 2: v0 = vandq_u8(vshrq_n_u8(qv0, 2), m03); v1 = vandq_u8(vshrq_n_u8(qv1, 2), m03); break;
1861+
case 4: v0 = vandq_u8(vshrq_n_u8(qv0, 4), m03); v1 = vandq_u8(vshrq_n_u8(qv1, 4), m03); break;
1862+
default: v0 = vshrq_n_u8(qv0, 6); v1 = vshrq_n_u8(qv1, 6); break;
1863+
}
1864+
/* Expand u8 → float32, accumulate dot and sum_x */
1865+
#define TQ_Q2K_ACC(nv, off, dl_v, ml_v) \
1866+
do { \
1867+
uint16x8_t w16_l = vmovl_u8(vget_low_u8(nv)); \
1868+
uint16x8_t w16_h = vmovl_u8(vget_high_u8(nv)); \
1869+
float32x4_t wf0 = vcvtq_f32_u32(vmovl_u16(vget_low_u16(w16_l))); \
1870+
float32x4_t wf1 = vcvtq_f32_u32(vmovl_u16(vget_high_u16(w16_l))); \
1871+
float32x4_t wf2 = vcvtq_f32_u32(vmovl_u16(vget_low_u16(w16_h))); \
1872+
float32x4_t wf3 = vcvtq_f32_u32(vmovl_u16(vget_high_u16(w16_h))); \
1873+
float32x4_t x0 = vld1q_f32(xp + (off)); \
1874+
float32x4_t x1 = vld1q_f32(xp + (off) + 4); \
1875+
float32x4_t x2 = vld1q_f32(xp + (off) + 8); \
1876+
float32x4_t x3 = vld1q_f32(xp + (off) + 12); \
1877+
float32x4_t vd = vdupq_n_f32(0.0f); \
1878+
vd = vfmaq_f32(vd, wf0, x0); \
1879+
vd = vfmaq_f32(vd, wf1, x1); \
1880+
vd = vfmaq_f32(vd, wf2, x2); \
1881+
vd = vfmaq_f32(vd, wf3, x3); \
1882+
float dot_s = vaddvq_f32(vd); \
1883+
float sum_s = vaddvq_f32(vaddq_f32(vaddq_f32(x0, x1), vaddq_f32(x2, x3))); \
1884+
sum += (dl_v) * dot_s - (ml_v) * sum_s; \
1885+
} while (0)
1886+
1887+
int yi = half * 128 + j * 32;
1888+
TQ_Q2K_ACC(v0, yi, dl0, ml0);
1889+
TQ_Q2K_ACC(v1, yi + 16, dl1, ml1);
1890+
#undef TQ_Q2K_ACC
1891+
#else
1892+
int yi = half * 128 + j * 32;
1893+
float dot0 = 0, sumx0 = 0;
1894+
for (int l = 0; l < 16; l++) {
1895+
float xv = xp[yi + l];
1896+
dot0 += (float)((q[l] >> shift) & 3) * xv;
1897+
sumx0 += xv;
1898+
}
1899+
sum += dl0 * dot0 - ml0 * sumx0;
1900+
1901+
float dot1 = 0, sumx1 = 0;
1902+
for (int l = 0; l < 16; l++) {
1903+
float xv = xp[yi + 16 + l];
1904+
dot1 += (float)((q[l + 16] >> shift) & 3) * xv;
1905+
sumx1 += xv;
1906+
}
1907+
sum += dl1 * dot1 - ml1 * sumx1;
1908+
#endif
1909+
shift += 2;
1910+
}
1911+
q += 32;
1912+
}
1913+
}
1914+
return sum;
1915+
}
1916+
18181917
static float fused_dot_q4_k(const void* row, const float* x, int n) {
18191918
const int nb = n / 256;
18201919
const block_q4_K* blk = (const block_q4_K*)row;
@@ -1846,22 +1945,79 @@ static float fused_dot_q4_k(const void* row, const float* x, int n) {
18461945
const float* xp = x + b * 256;
18471946
int is = 0;
18481947

1849-
/* 4 groups of 64 elements */
1948+
#if TQ_HAS_NEON
1949+
/* 4 groups of 64 elements, NEON-accelerated */
1950+
const uint8x16_t mask_lo = vdupq_n_u8(0x0F);
1951+
for (int j = 0; j < 256; j += 64) {
1952+
const float d1 = d * sc[is + 0];
1953+
const float m1 = dmin * mn[is + 0];
1954+
const float d2 = d * sc[is + 1];
1955+
const float m2 = dmin * mn[is + 1];
1956+
1957+
/* Load 32 bytes = 32 pairs of nibbles covering 64 elements */
1958+
uint8x16_t qa = vld1q_u8(q);
1959+
uint8x16_t qb = vld1q_u8(q + 16);
1960+
/* Extract low nibbles (→ elements 0..31) and high nibbles (→ 32..63) */
1961+
uint8x16_t lo_a = vandq_u8(qa, mask_lo);
1962+
uint8x16_t lo_b = vandq_u8(qb, mask_lo);
1963+
uint8x16_t hi_a = vshrq_n_u8(qa, 4);
1964+
uint8x16_t hi_b = vshrq_n_u8(qb, 4);
1965+
1966+
/* Convert u8 nibbles [0..15] to float32 and dot with xp[...] */
1967+
float32x4_t vdot1 = vdupq_n_f32(0.0f);
1968+
float32x4_t vsum1 = vdupq_n_f32(0.0f);
1969+
float32x4_t vdot2 = vdupq_n_f32(0.0f);
1970+
float32x4_t vsum2 = vdupq_n_f32(0.0f);
1971+
/* Helper: process 16 elements of x[off:off+16] with nibble vector `nv` */
1972+
#define TQ_Q4K_ACC(nv, off, vdot, vsum) \
1973+
do { \
1974+
uint16x8_t w16_l = vmovl_u8(vget_low_u8(nv)); \
1975+
uint16x8_t w16_h = vmovl_u8(vget_high_u8(nv)); \
1976+
float32x4_t wf0 = vcvtq_f32_u32(vmovl_u16(vget_low_u16(w16_l))); \
1977+
float32x4_t wf1 = vcvtq_f32_u32(vmovl_u16(vget_high_u16(w16_l))); \
1978+
float32x4_t wf2 = vcvtq_f32_u32(vmovl_u16(vget_low_u16(w16_h))); \
1979+
float32x4_t wf3 = vcvtq_f32_u32(vmovl_u16(vget_high_u16(w16_h))); \
1980+
float32x4_t x0 = vld1q_f32(xp + (off)); \
1981+
float32x4_t x1 = vld1q_f32(xp + (off) + 4); \
1982+
float32x4_t x2 = vld1q_f32(xp + (off) + 8); \
1983+
float32x4_t x3 = vld1q_f32(xp + (off) + 12); \
1984+
(vdot) = vfmaq_f32((vdot), wf0, x0); \
1985+
(vdot) = vfmaq_f32((vdot), wf1, x1); \
1986+
(vdot) = vfmaq_f32((vdot), wf2, x2); \
1987+
(vdot) = vfmaq_f32((vdot), wf3, x3); \
1988+
(vsum) = vaddq_f32((vsum), vaddq_f32(vaddq_f32(x0, x1), vaddq_f32(x2, x3))); \
1989+
} while (0)
1990+
TQ_Q4K_ACC(lo_a, j + 0, vdot1, vsum1);
1991+
TQ_Q4K_ACC(lo_b, j + 16, vdot1, vsum1);
1992+
TQ_Q4K_ACC(hi_a, j + 32, vdot2, vsum2);
1993+
TQ_Q4K_ACC(hi_b, j + 48, vdot2, vsum2);
1994+
#undef TQ_Q4K_ACC
1995+
1996+
float dot1_s = vaddvq_f32(vdot1);
1997+
float sum1_s = vaddvq_f32(vsum1);
1998+
float dot2_s = vaddvq_f32(vdot2);
1999+
float sum2_s = vaddvq_f32(vsum2);
2000+
sum += d1 * dot1_s - m1 * sum1_s;
2001+
sum += d2 * dot2_s - m2 * sum2_s;
2002+
2003+
q += 32;
2004+
is += 2;
2005+
}
2006+
#else
2007+
/* Scalar fallback (non-ARM) */
18502008
for (int j = 0; j < 256; j += 64) {
18512009
const float d1 = d * sc[is + 0];
18522010
const float m1 = dmin * mn[is + 0];
18532011
const float d2 = d * sc[is + 1];
18542012
const float m2 = dmin * mn[is + 1];
18552013

1856-
/* First 32 elements: low nibble */
18572014
float dot1 = 0.0f, sum_x1 = 0.0f;
18582015
for (int l = 0; l < 32; l++) {
18592016
dot1 += (float)(q[l] & 0x0F) * xp[j + l];
18602017
sum_x1 += xp[j + l];
18612018
}
18622019
sum += d1 * dot1 - m1 * sum_x1;
18632020

1864-
/* Next 32 elements: high nibble */
18652021
float dot2 = 0.0f, sum_x2 = 0.0f;
18662022
for (int l = 0; l < 32; l++) {
18672023
dot2 += (float)(q[l] >> 4) * xp[j + 32 + l];
@@ -1872,6 +2028,7 @@ static float fused_dot_q4_k(const void* row, const float* x, int n) {
18722028
q += 32;
18732029
is += 2;
18742030
}
2031+
#endif
18752032
}
18762033
return sum;
18772034
}
@@ -2416,6 +2573,9 @@ void tq_matmul_gguf(float* out, const float* x,
24162573
case TQ_GGML_TYPE_Q8_0:
24172574
fused_dot = fused_dot_q8_0;
24182575
break;
2576+
case TQ_GGML_TYPE_Q2_K:
2577+
fused_dot = fused_dot_q2_k;
2578+
break;
24192579
case TQ_GGML_TYPE_Q8_1:
24202580
fused_dot = fused_dot_q8_1;
24212581
break;

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