put this in your autoexec or config.cfg:
host_threaded_mode "2"
mat_queue_mode "1"
cl_threaded_bone_setup "1"
cl_threaded_client_leaf_system "1"
r_threaded_client_shadow_manager "1"
r_threaded_particles "1"
r_threaded_renderables "1"
and add this to your launch options:
+host_threaded_mode 2