This blog post will explain how to use multiple CPUS with QEMU. The -smp flag will be used to determine how many sockets, cores, and threads QEMU can use. Sockets also means CPUs. In order to use more than one thread, the host CPU has to be able to support hyperthreading. To get the amount of threads each socket can use, multiply cores and threads to get two threads for each socket. Multiply that result by the amount of sockets to get the total amount of CPU threads QEMU can use.
-smp sockets=2,cores=2,threads=1The Windows version of QEMU was used to write this blog post.