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llama.cpp/ggml/src/ggml-vulkan/vulkan-shaders/flash_attn.comp
Jeff Bolz 94e82c7ead vulkan: clamp matmul and FA results to the max finite value (#15652)
* vulkan: clamp matmul and FA results to the max finite value

* only clamp for fp16
2025-08-31 08:27:57 +02:00

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#version 450
#extension GL_EXT_control_flow_attributes : enable
#extension GL_EXT_shader_16bit_storage : require
#extension GL_EXT_shader_explicit_arithmetic_types_float16 : require
#extension GL_EXT_shader_explicit_arithmetic_types_int32 : require
#extension GL_KHR_shader_subgroup_shuffle : enable
#include "types.comp"
#include "flash_attn_base.comp"
const uint32_t HSK_per_thread = HSK / D_split;
const uint32_t HSV_per_thread = HSV / D_split;
const uint32_t cols_per_iter = WorkGroupSize / D_split;
const uint32_t cols_per_thread = Bc / cols_per_iter;
layout (binding = 0) readonly buffer Q {float data_q[];};
layout (binding = 0) readonly buffer QV4 {vec4 data_qv4[];};
layout (binding = 1) readonly buffer K {float16_t data_k[];};
layout (binding = 1) readonly buffer KV4 {f16vec4 data_kv4[];};
layout (binding = 2) readonly buffer V {float16_t data_v[];};
layout (binding = 2) readonly buffer VV4 {f16vec4 data_vv4[];};
layout (binding = 3) readonly buffer M {float16_t data_m[];};
// Store the output when doing grouped query attention.
// Rows index by Q's dimension 2, and the first N rows are valid.
D_TYPE perElemOpGqaStore(const in uint32_t r, const in uint32_t c, const in D_TYPE elem, const in uint32_t o_offset, const in uint32_t iq2, const in uint32_t N)
{
uint32_t offset = (iq2 + r) * HSV + c;
data_o[o_offset + offset] = D_TYPE(elem);
return elem;
}
shared FLOAT_TYPE tmpsh[WorkGroupSize];
shared vec4 tmpshv4[WorkGroupSize];
shared float masksh[Bc][Br];
shared vec4 Qf[Br][HSK / 4];
void main() {
#ifdef NEEDS_INIT_IQ_SHMEM
init_iq_shmem(gl_WorkGroupSize);
#endif
init_indices();
const uint32_t tid = gl_LocalInvocationIndex;
const uint32_t d_tid = gl_LocalInvocationIndex % D_split;
const uint32_t col_tid = gl_LocalInvocationIndex / D_split;
uint32_t q_offset = (iq2*p.nb02+iq3*p.nb03) / 4;
[[unroll]] for (uint32_t idx = 0; idx < Br * HSK / 4; idx += gl_WorkGroupSize.x) {
uint32_t d = (idx + tid) % (HSK / 4);
uint32_t r = (idx + tid) / (HSK / 4);
if (r < Br && d < HSK / 4 &&
i * Br + r < N) {
Qf[r][d] = vec4(data_qv4[q_offset / 4 + (i * Br + r) * q_stride / 4 + d]) * p.scale;
}
}
barrier();
vec4 Of[Br][HSV_per_thread / 4];
[[unroll]] for (uint32_t d = 0; d < HSV_per_thread / 4; ++d) {
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
Of[r][d] = vec4(0.0);
}
}
float Lf[Br], Mf[Br];
// Use -FLT_MAX/2 rather than -inf to reduce the possibility of NaNs, e.g. when computing Mold-M.
const float NEG_FLT_MAX_OVER_2 = uintBitsToFloat(0xFEFFFFFF);
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
Lf[r] = 0;
Mf[r] = NEG_FLT_MAX_OVER_2;
}
float slope[Br];
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
slope[r] = 1.0;
}
// ALiBi
if (p.max_bias > 0.0f) {
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
slope[r] = perElemOpComputeSlope(r, col_tid, ACC_TYPE(0), iq2);
}
}
#if BLOCK_SIZE > 1
uint32_t k_offset = (ik2*p.nb12 + ik3*p.nb13) / BLOCK_BYTE_SIZE;
uint32_t v_offset = (iv2*p.nb22 + iv3*p.nb23) / BLOCK_BYTE_SIZE;
#else
uint32_t k_offset = (ik2*p.nb12 + ik3*p.nb13) / 2;
uint32_t v_offset = (iv2*p.nb22 + iv3*p.nb23) / 2;
#endif
uint32_t m_offset = 0;
if (p.nem2 != 1 || p.nem3 != 1) {
m_offset = ((iq3 % p.nem3) * p.nem2 + (iq2 % p.nem2)) * p.nem1 * KV;
}
[[dont_unroll]]
for (uint32_t j = start_j; j < end_j; ++j) {
float Sf[Br][cols_per_thread];
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
[[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
Sf[r][c] = 0.0;
}
}
[[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
[[unroll]] for (uint32_t d = 0; d < HSK_per_thread / 4; ++d) {
#if BLOCK_SIZE > 1
uint coord = (j * Bc + c * cols_per_iter + col_tid) * k_stride * BLOCK_SIZE + 4 * (d * D_split + d_tid);
uint ib = coord / BLOCK_SIZE;
uint iqs = (coord % BLOCK_SIZE);
vec4 K_Tf = dequantize4(ib, iqs, k_offset, BINDING_IDX_K);
#else
vec4 K_Tf = vec4(data_kv4[k_offset / 4 + (j * Bc + c * cols_per_iter + col_tid) * k_stride / 4 + d * D_split + d_tid]);
#endif
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
Sf[r][c] += dot(Qf[r][d * D_split + d_tid], K_Tf);
}
}
}
[[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
// Compute sum across the D_split
[[unroll]] for (uint s = D_split / 2; s > 0; s >>= 1) {
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
Sf[r][c] += subgroupShuffleXor(Sf[r][c], s);
}
}
}
if (p.logit_softcap != 0.0f) {
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
[[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
Sf[r][c] = p.logit_softcap * tanh(Sf[r][c]);
}
}
}
if ((p.mask_n_head_log2 & MASK_ENABLE_BIT) != 0) {
[[unroll]] for (uint32_t idx = 0; idx < Bc * Br; idx += gl_WorkGroupSize.x) {
uint32_t c = (idx + tid) % Bc;
uint32_t r = (idx + tid) / Bc;
if (idx + tid < Bc * Br) {
masksh[c][r] = float(data_m[m_offset + (i * Br + r) * m_stride + (j * Bc + c)]);
}
}
barrier();
[[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
float mvf = masksh[c * cols_per_iter + col_tid][r];
Sf[r][c] += slope[r]*mvf;
}
}
barrier();
}
float rowmaxf[Br], Pf[Br][cols_per_thread], rowsumf[Br], eMf[Br], Moldf[Br];
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
rowmaxf[r] = Sf[r][0];
[[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
rowmaxf[r] = max(rowmaxf[r], Sf[r][c]);
}
Moldf[r] = Mf[r];
// M = max(rowmax, Mold)
// P = e^(S - M)
// eM = e^(Mold - M)
Mf[r] = max(rowmaxf[r], Moldf[r]);
[[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
Pf[r][c] = exp(Sf[r][c] - Mf[r]);
}
eMf[r] = exp(Moldf[r] - Mf[r]);
// Compute sum across row of P
rowsumf[r] = 0.0;
[[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
rowsumf[r] += Pf[r][c];
}
Lf[r] = eMf[r]*Lf[r] + rowsumf[r];
}
[[unroll]] for (uint32_t d = 0; d < HSV_per_thread / 4; ++d) {
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
Of[r][d] = eMf[r] * Of[r][d];
}
}
[[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
[[unroll]] for (uint32_t d = 0; d < HSV_per_thread / 4; ++d) {
#if BLOCK_SIZE > 1
uint coord = (j * Bc + c * cols_per_iter + col_tid) * v_stride * BLOCK_SIZE + 4 * (d * D_split + d_tid);
uint ib = coord / BLOCK_SIZE;
uint iqs = (coord % BLOCK_SIZE);
vec4 Vf = dequantize4(ib, iqs, v_offset, BINDING_IDX_V);
#else
vec4 Vf = vec4(data_vv4[v_offset / 4 + (j * Bc + c * cols_per_iter + col_tid) * v_stride / 4 + d * D_split + d_tid]);
#endif
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
Of[r][d] += Pf[r][c] * Vf;
}
}
}
barrier();
}
// reduce across threads
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
float rowmaxf, eMf;
tmpsh[tid] = Mf[r];
// Compute max across the row
barrier();
[[unroll]] for (int s = int(gl_WorkGroupSize.x) / 2; s >= D_split; s >>= 1) {
if (tid < s) {
tmpsh[tid] = max(tmpsh[tid], tmpsh[tid + s]);
}
barrier();
}
rowmaxf = tmpsh[d_tid];
barrier();
float Moldf = Mf[r];
// M = max(rowmax, Mold)
// eM = e^(Mold - M)
Mf[r] = max(rowmaxf, Moldf);
eMf = exp(Moldf - Mf[r]);
Lf[r] = eMf*Lf[r];
tmpsh[tid] = Lf[r];
// Compute sum across the row
barrier();
[[unroll]] for (int s = int(gl_WorkGroupSize.x) / 2; s >= D_split; s >>= 1) {
if (tid < s) {
tmpsh[tid] = tmpsh[tid] + tmpsh[tid + s];
}
barrier();
}
Lf[r] = tmpsh[d_tid];
barrier();
[[unroll]] for (uint32_t d = 0; d < HSV_per_thread / 4; ++d) {
Of[r][d] = eMf * Of[r][d];
tmpshv4[tid] = Of[r][d];
barrier();
[[unroll]] for (int s = int(gl_WorkGroupSize.x) / 2; s >= D_split; s >>= 1) {
if (tid < s) {
Of[r][d] += tmpshv4[tid + s];
tmpshv4[tid] = Of[r][d];
}
barrier();
}
Of[r][d] = tmpshv4[d_tid];
barrier();
}
}
// If there is split_k, then the split_k resolve shader does the final
// division by L. Store the intermediate O value and per-row m and L values.
if (p.k_num > 1) {
uint32_t o_offset = HSV * p.ne1 * (split_k_index + iq3 * p.k_num);
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
if (r < N) {
[[unroll]] for (uint32_t d = 0; d < HSV_per_thread / 4; ++d) {
[[unroll]] for (uint32_t comp = 0; comp < 4; ++comp) {
perElemOpGqaStore(r, 4*(d * D_split + d_tid) + comp, Of[r][d][comp], o_offset, iq2, N);
}
}
}
}
o_offset = HSV * p.ne1 * p.ne3 * p.k_num + p.ne1 * (split_k_index + iq3 * p.k_num) * 2;
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
if (r < N) {
perElemOpStoreCol0(r, 0u, ACC_TYPE(Lf[r]), o_offset, iq2, N);
perElemOpStoreCol0(r, 0u, ACC_TYPE(Mf[r]), o_offset + p.ne1, iq2, N);
}
}
return;
}
if ((p.mask_n_head_log2 & SINK_ENABLE_BIT) != 0) {
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
float sink = perElemOpGetSink(r, 0u, ACC_TYPE(0), iq2);
float ms = 1.0f;
float vs = 1.0f;
if (sink > Mf[r]) {
ms = exp(Mf[r] - sink);
[[unroll]] for (uint32_t d = 0; d < HSV_per_thread / 4; ++d) {
Of[r][d] *= ms;
}
} else {
vs = exp(sink - Mf[r]);
}
Lf[r] = Lf[r]*ms + vs;
}
}
float Lfrcp[Br];
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
Lfrcp[r] = 1.0 / Lf[r];
}
[[unroll]] for (uint32_t d = 0; d < HSV_per_thread / 4; ++d) {
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
Of[r][d] *= Lfrcp[r];
#if defined(ACC_TYPE_MAX)
Of[r][d] = clamp(Of[r][d], -vec4(ACC_TYPE_MAX), vec4(ACC_TYPE_MAX));
#endif
}
}
uint32_t o_offset = iq3*p.ne2*p.ne1*HSV;
if (p.gqa_ratio > 1) {
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
if (r < N) {
[[unroll]] for (uint32_t d = 0; d < HSV_per_thread / 4; ++d) {
[[unroll]] for (uint32_t comp = 0; comp < 4; ++comp) {
perElemOpGqaStore(r, 4*(d * D_split + d_tid) + comp, Of[r][d][comp], o_offset, iq2, N);
}
}
}
}
} else {
[[unroll]] for (uint32_t r = 0; r < Br; ++r) {
if (i * Br + r < N) {
[[unroll]] for (uint32_t d = 0; d < HSV_per_thread / 4; ++d) {
[[unroll]] for (uint32_t comp = 0; comp < 4; ++comp) {
data_o[o_offset + iq2 * HSV + (i * Br + r) * p.ne1 * HSV + 4*(d * D_split + d_tid) + comp] = D_TYPE(Of[r][d][comp]);
}
}
}
}
}
}