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#version 450
#extension GL_EXT_control_flow_attributes : enable
layout (push_constant) uniform parameter
{
uint KX;
uint KY;
uint ne00;
uint ne01;
uint ne02;
uint ne12;
uint ne13;
uint nb11;
uint nb12;
uint nb13;
float scale;
float max_bias;
float m0;
float m1;
uint n_head_log2;
uint nrows_x;
} p;
#include "types.comp"
layout(constant_id = 0) const uint BLOCK_SIZE = 32;
layout(local_size_x_id = 0, local_size_y = 1, local_size_z = 1) in;
layout (binding = 0) readonly buffer X {A_TYPE data_a[];};
layout (binding = 1) readonly buffer Y {B_TYPE data_b[];};
layout (binding = 2) buffer D {D_TYPE data_d[];};
shared FLOAT_TYPE vals[BLOCK_SIZE];
// num_iters is the number of BLOCK_SIZE loop iterations we need to iterate
// over all the columns. The main function tries to pass a constant here,
// as if it were a template function, to allow unrolling.
void soft_max(uint num_iters) {
const uint tid = gl_LocalInvocationID.x;
const uint rowx = gl_WorkGroupID.z * 262144 + gl_WorkGroupID.y * 512 + gl_WorkGroupID.x;
const uint32_t i03 = rowx / (p.ne01 * p.ne02);
const uint32_t i02 = (rowx - i03 * p.ne01 * p.ne02) / p.ne01;
const uint32_t i01 = rowx % p.ne01;
uint rowy_start = 0;
if (p.KY > 0) {
rowy_start = i01 * p.nb11 + (i02 % p.ne12) * p.nb12 + (i03 % p.ne13) * p.nb13;
}
if (rowx >= p.nrows_x) {
return;
}
float slope = 1.0f;
// ALiBi
if (p.max_bias > 0.0f) {
const uint h = (rowx / p.ne01) % p.ne02; // head index
const float base = h < p.n_head_log2 ? p.m0 : p.m1;
const uint exp = h < p.n_head_log2 ? h + 1 : 2*(h - p.n_head_log2) + 1;
slope = pow(base, exp);
}
// Find max
FLOAT_TYPE max_val = uintBitsToFloat(0xFF800000);
// Cache values while we compute the max, so we don't need to read them
// again when we're ready to compute exp(x-max).
const uint DATA_CACHE_SIZE = 16;
FLOAT_TYPE data_cache[DATA_CACHE_SIZE];
[[unroll]] for (uint col0 = 0, idx = 0; idx < num_iters; col0 += BLOCK_SIZE, ++idx) {
const uint col = col0 + tid;
FLOAT_TYPE a = FLOAT_TYPE(0);
if (col < p.KX) {
a = data_a[rowx * p.KX + col];
}
FLOAT_TYPE b = FLOAT_TYPE(0);
if (p.KY > 0 && col < p.KX) {
b = data_b[rowy_start + col];
}
FLOAT_TYPE v = a * p.scale + slope * b;
if (col < p.KX) {
max_val = max(max_val, v);
}
if (idx < DATA_CACHE_SIZE) {
data_cache[idx] = v;
}
}
// reduce across the workgroup
vals[tid] = max_val;
barrier();
[[unroll]] for (uint s = BLOCK_SIZE / 2; s > 0; s >>= 1) {
if (tid < s) {
vals[tid] = max(vals[tid], vals[tid + s]);
}
barrier();
}
max_val = vals[0];
barrier();
FLOAT_TYPE sum = FLOAT_TYPE(0.0f);
// Compute sum{exp(x - max)}
[[unroll]] for (uint col0 = 0, idx = 0; idx < num_iters; col0 += BLOCK_SIZE, ++idx) {
const uint col = col0 + tid;
if (col >= p.KX) {
break;
}
// compute exp(a*scale+b*slope), add it to sum, and cache the new value
// in data_cache if possible.
const uint i = rowx * p.KX + col;
FLOAT_TYPE val;
if (idx < DATA_CACHE_SIZE) {
val = exp(data_cache[idx] - max_val);
} else {
val = exp(FLOAT_TYPE(data_a[i]) * p.scale + (p.KY > 0 ? slope * FLOAT_TYPE(data_b[rowy_start + col]) : FLOAT_TYPE(0.0f)) - max_val);
}
sum += val;
if (idx < DATA_CACHE_SIZE) {
data_cache[idx] = val;
} else {
data_d[i] = D_TYPE(val);
}
}
// reduce across the workgroup
vals[tid] = sum;
barrier();
[[unroll]] for (uint s = BLOCK_SIZE / 2; s > 0; s >>= 1) {
if (tid < s) {
vals[tid] += vals[tid + s];
}
barrier();
}
sum = vals[0];
FLOAT_TYPE rcpdivisor = 1.0/sum;
[[unroll]] for (uint col0 = 0, idx = 0; idx < num_iters; col0 += BLOCK_SIZE, ++idx) {
const uint col = col0 + tid;
if (col >= p.KX) {
continue;
}
if (idx < DATA_CACHE_SIZE) {
data_d[rowx*p.KX + col] = D_TYPE(data_cache[idx] * rcpdivisor);
} else {
data_d[rowx*p.KX + col] *= D_TYPE(rcpdivisor);
}
}
}
void main() {
// instantiate the soft_max function for several different
// dimensions, to allow loop unrolling
uint num_blocks = (p.KX + BLOCK_SIZE - 1) / BLOCK_SIZE;
if (num_blocks > 32) {
soft_max(num_blocks);
} else if (num_blocks > 16) {
soft_max(32);
} else if (num_blocks > 8) {
soft_max(16);
} else if (num_blocks > 4) {
soft_max(8);
} else if (num_blocks == 4) {
soft_max(4);
} else if (num_blocks == 3) {
soft_max(3);
} else if (num_blocks == 2) {
soft_max(2);
} else if (num_blocks == 1) {
soft_max(1);
}
}
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