\[ x y'(x)-y(x) f(x y(x))=0 \] ✓ Mathematica : cpu = 0.182382 (sec), leaf count = 115
DSolve[-(f[x*y[x]]*y[x]) + x*Derivative[1][y][x] == 0,y[x],x]
\[\text {Solve}\left [\int _1^{y(x)}\left (\frac {1}{(-f(x K[2])-1) K[2]}-\int _1^x\left (\frac {f'(K[1] K[2])}{f(K[1] K[2])+1}-\frac {f(K[1] K[2]) f'(K[1] K[2])}{(f(K[1] K[2])+1)^2}\right )dK[1]\right )dK[2]+\int _1^x\frac {f(K[1] y(x))}{(f(K[1] y(x))+1) K[1]}dK[1]=c_1,y(x)\right ]\] ✓ Maple : cpu = 0.028 (sec), leaf count = 29
dsolve(x*diff(y(x),x)-y(x)*f(x*y(x)) = 0,y(x))
\[y \left (x \right ) = \frac {\RootOf \left (-\ln \left (x \right )+c_{1}+\int _{}^{\textit {\_Z}}\frac {1}{\textit {\_a} \left (1+f \left (\textit {\_a} \right )\right )}d \textit {\_a} \right )}{x}\]