I did set hw.smt=1 and all are shown now "online". I'm a little bit worry since I switched to this cpu from a 2 core AMD. Total mess in the CPU manufacturer yard. But we cannot produce our own cpu in the kitchen, can't we?
# sysctl hw.smt=1 hw.smt: 0 -> 1 hw.machine=amd64 hw.model=AMD A8-5500B APU with Radeon(tm) HD Graphics hw.ncpu=4 hw.byteorder=1234 hw.pagesize=4096 hw.disknames=sd0:b10ceaa38ac5ec4d,cd0: hw.diskcount=2 hw.sensors.km0.temp0=0.00 degC hw.cpuspeed=3200 hw.setperf=100 hw.vendor=Hewlett-Packard hw.product=HP Compaq Pro 6305 SFF hw.serialno=CZC3515JBD hw.uuid=809987e8-6e63-e311-8653-fb3620fd442c hw.physmem=7711543296 hw.usermem=7711526912 hw.ncpufound=4 hw.allowpowerdown=1 hw.perfpolicy=auto hw.smt=1 hw.ncpuonline=4 hw.power=1
