  We determine non-perturbatively the normalisation constant Z_m*Z_P/Z_A as
well as the Symanzik coefficients b_m and b_A-b_P, required in O(a) improved
quark mass renormalisation with Wilson fermions. The strategy underlying their
computation involves simulations in N_f=3 QCD with O(a) improved massless sea
and non-degenerate valence quarks in the finite-volume Schroedinger functional
scheme. Our results, which cover the typical gauge coupling range of
large-volume N_f=2+1 QCD simulations with Wilson fermions at lattice spacings
below 0.1 fm, are of particular use for the non-perturbative calculation of
O(a) improved renormalised quark masses.
