  We investigate the spin relaxation of $p$-type GaAs quantum wires by
numerically solving the fully microscopic kinetic spin Bloch equations. We find
that the quantum-wire size influences the spin relaxation time effectively by
modulating the energy spectrum and the heavy-hole--light-hole mixing of wire
states. The effects of quantum-wire size, temperature, hole density, and
initial polarization are investigated in detail. We show that, depending on the
situation, the spin relaxation time can either increase or decrease with hole
density. Due to the different subband structure and effects arising from
spin-orbit coupling, many spin-relaxation properties are quite different from
those of holes in the bulk or in quantum wells, and the inter-subband
scattering makes a marked contribution to the spin relaxation.
