The crew at Phoronix is investigating the benefits of using SMP with the latest v1.2.1 patch for Quake 4 under Linux. They didn't have much luck though. Our experience in a Windows environment was much more positive, however. In CPU-bound situations, enabling SMP with Q4 under Windows resulted in some significant performance gains.
"Released earlier today was the Quake 4 v1.2.1 point release patch. The major feature to come down the pipeline in Quake 4 v1.2.1 is Hyper-Threading Technology and dual-core support for the Linux binaries. With Quake 4 now supporting Hyper-Threading and dual-core processors, players should expect to find significant performance gains when gaming. Two of the numbers that id Software have stated is a 25% performance jump compared to non Intel Hyper-Threaded CPUs and dual core processors should experience somewhere in the ballpark of a 87% performance boost. At Phoronix, we have examined these performance situations using an Intel Pentium D and Intel Pentium 4 HT CPUs to get a better idea as to what can be expected from upcoming multi-threaded games."