\[ \boxed { \left ( {\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) \right ) y \left ( x \right ) - \left ( {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) \right ) ^{2}+f \left ( x \right ) {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) - \left ( {\frac {\rm d}{{\rm d}x}}f \left ( x \right ) \right ) y \left ( x \right ) - \left ( y \left ( x \right ) \right ) ^{3}=0} \]
Mathematica: cpu = 0.244531 (sec), leaf count = 43 \[ \text {DSolve}\left [-y(x) f'(x)+f(x) y'(x)+y(x) y''(x)-y'(x)^2-y(x)^3=0,y(x),x\right ] \]
Maple: cpu = 0.375 (sec), leaf count = 0 \[ \text {could not solve} \]