  We calculate on GPUs the disconnected diagrams associated with the nucleon
form factors and moments of generalized parton distributions using Nf=2+1+1
twisted mass fermions. We employ the truncated solver method (TSM) for
estimating the all-to-all propagators. Due to the fact that the TSM involves
many low precision stochastic estimators, the usage of GPUs is essential to
perform efficiently the contractions and the inversions.
