diff --git a/ggml/src/ggml-cuda/fattn-common.cuh b/ggml/src/ggml-cuda/fattn-common.cuh index 09c19429ad..3144678728 100644 --- a/ggml/src/ggml-cuda/fattn-common.cuh +++ b/ggml/src/ggml-cuda/fattn-common.cuh @@ -11,10 +11,12 @@ #define SOFTMAX_FTZ_THRESHOLD -20.0f // Softmax exp. of values smaller than this are flushed to zero to avoid NaNs. // log(2) = 0.6931, by adding this to the KQ maximum used for the softmax the numerical range representable -// by the VKQ accumulators is effectively being shifted up by a factor of 8. +// by the VKQ accumulators is effectively being shifted up by a factor of 2. // This reduces issues with numerical overflow but also causes larger values to be flushed to zero. // However, as the output from FlashAttention will usually be used as an input for a matrix multiplication this should be negligible. -#define FATTN_KQ_MAX_OFFSET 0.6931f +// Still, the value range should be shifted as much as necessary but as little as possible. +// The macro on the following line shifts it by a factor of 2**3=8, as was needed to fix https://github.com/ggml-org/llama.cpp/issues/18606 . +#define FATTN_KQ_MAX_OFFSET (3.0f*0.6931f) typedef void (* fattn_kernel_t)( const char * __restrict__ Q,