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numerics: saturate the prompt path's FP16 SwiGLU products; log1pf in the unfused GDN gate #281

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numerics: saturate the prompt path's FP16 SwiGLU products; log1pf in the unfused GDN gate #281

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2 changes: 1 addition & 1 deletion src/kernels/cuda/native_gdn_preprocess.cu
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Original file line number Diff line number Diff line change
Expand Up @@ -92,7 +92,7 @@ __global__ void gate_softplus(const float* __restrict__ alpha, const float* __re
const int i = blockIdx.x * blockDim.x + threadIdx.x;
if (i >= count) return;
const float value = __fadd_rn(alpha[i], dt[i]);
const float softplus = value > 20.0f ? value : logf(1.0f + expf(value));
const float softplus = value > 20.0f ? value : log1pf(expf(value)); // 1 + e^v loses e^v below ~1e-7
gate[i] = softplus * ssm_a[i];
}

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7 changes: 5 additions & 2 deletions src/prefill/kernels.cu
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Expand Up @@ -34,6 +34,9 @@ __device__ __forceinline__ uint16_t bf(float f) {
}
__device__ __forceinline__ float sigm(float x) { return 1.0f / (1.0f + __expf(-x)); }
__device__ __forceinline__ uint16_t hf(float f) { return __half_as_ushort(__float2half_rn(f)); }
// A SwiGLU product for an FP16 GEMM: saturated, so a token with a massive activation cannot turn into inf and then
// NaN in the down projection (decode's q8_1 has room to ~8e6; FP16 ends at 65504)
__device__ __forceinline__ uint16_t hf_sat(float f) { return hf(fminf(fmaxf(f, -65504.0f), 65504.0f)); }
// block-wide sum for blockDim.x <= 1024, result broadcast
__device__ float block_sum(float v, float* sh) {
const int lane = threadIdx.x & 31, w = threadIdx.x >> 5;
Expand Down Expand Up @@ -486,14 +489,14 @@ __global__ void swiglu_il_kernel(const float* __restrict__ gu, uint16_t* __restr
if (i >= n * 640) return;
const int64_t r = i / 640, k = i % 640;
const float g = gu[r * 1280 + 2 * k], u = gu[r * 1280 + 2 * k + 1];
h16[i] = hf(g / (1.0f + __expf(-g)) * u);
h16[i] = hf_sat(g / (1.0f + __expf(-g)) * u);
}
__global__ void swiglu_pair_kernel(const float* __restrict__ g, const float* __restrict__ u, uint16_t* __restrict__ h16,
int64_t n) {
const int64_t i = (int64_t) blockIdx.x * blockDim.x + threadIdx.x;
if (i >= n * 640) return;
const float a = g[i];
h16[i] = hf(a / (1.0f + __expf(-a)) * u[i]);
h16[i] = hf_sat(a / (1.0f + __expf(-a)) * u[i]);
}
__global__ void gather_rows16_kernel(const uint16_t* __restrict__ x, const int32_t* __restrict__ src,
uint16_t* __restrict__ dst, int64_t n, int64_t width) {
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