Hercules (emulator) - Performance

Performance

It is difficult to determine exactly how Hercules emulation performance corresponds to real mainframe hardware, but the performance characteristics are understandably quite different. This is partially due to the difficulty of comparing real mainframe hardware to other PCs and servers as well as the lack of concrete, controlled performance comparisons. Performance comparisons are likely legally impossible for licensed IBM operating systems, and those operating systems are quite different than other operating systems, such as Linux.

Hercules expresses its processing performance in MIPS. Due to the age of the earlier System/360 and System/370 hardware, it is a relatively safe assumption that Hercules will outperform them when running on moderately powerful hardware, despite the considerable overhead of emulating a computer architecture in software. However, newer, partially or fully configured System z machines outperform Hercules by a wide margin. A relatively fast dual processor X86 machine running Hercules is capable of sustaining about 50 to 60 MIPS for code that utilizes both processors in a realistic environment, with sustained rates rising to a reported 300 MIPS on leading-edge (early 2009) PC-class systems. Hercules can produce peaks of over 1200 MIPS when running in a tight loop, such as in a synthetic instruction benchmark or with other small, compute-intensive programs.

Tom Lehmann, co-founder of TurboHercules, wrote:

... We can run a reasonably sized load (800 MIPS with our standard package). If the machine in question is larger than that, we can scale to 1600 MIPS with our quad Nehalem based package, and we have been promised an 8 way Nehalem EX based machine early next year that should take us to the 3200 MIPS mark. Anything bigger than that is replicated by a collection of systems.

Hercules generally outperforms IBM's PC based mainframes from the mid-1990s, which have an advertised peak performance of around 29 MIPS. Compared to the more powerful but still entry-level IBM Multiprise 2000 and 3000 mainframes (also from the 1990s), Hercules on typical X86 hardware would be considered a mid-range server in performance terms. For every mainframe after the 9672 Generation 1, Hercules would generally be the lowest end system. For comparison, current high-end IBM zEnterprise 196 systems can deliver over 52,000 MIPS per machine, and they have considerable I/O performance advantages.

Note that there are other non-functional system attributes beyond performance which are typically relevant to mainframe operators.