Introducing PTLsim

PTLsim is a cycle accurate x86 microprocessor simulator and virtual machine for the x86 and x86-64 instruction sets. PTLsim models a modern superscalar out of order x86-64 compatible processor core at a configurable level of detail ranging from full-speed native execution on the host CPU all the way down to RTL level models of all key pipeline structures. In addition, all microcode, the complete cache hierarchy, memory subsystem and supporting hardware devices are modeled with true cycle accuracy. PTLsim supports the full x86-64 instruction set of the Pentium 4+, Athlon 64 and similar machines with all extensions (x86-64, SSE/SSE2/SSE3, MMX, x87). It is currently the only tool available to the public to support true cycle accurate modeling of real x86 microarchitectures.

PTLsim is very different from most cycle accurate simulators used in research applications. It runs directly on the same platform it is simulating (an x86-64 or x86 machine running Linux) and is able to switch in and out of full out of order simulation mode and native x86-64 mode at any time completely transparent to the running user code. This lets users quickly profile a small section of the user code without the overhead of emulating the uninteresting parts. PTLsim runs unmodified 32-bit x86 and 64-bit x86-64 applications without special compilers or toolchains.

PTLsim comes in two flavors. The standard version runs any 32-bit or 64-bit single threaded userspace Linux application. PTLsim/X integrates with the Xen hypervisor to provide full system x86-64 simulation, multi-processor and multi-threading support, cycle accurate device and timing models, and much more.

Compared to competing simulators, PTLsim provides extremely high performance even when running in full cycle accurate out of order simulation mode. Even with its optimized core, PTLsim still allows a significant amount of flexibility for easy experimentation.

PTLsim is used extensively in our Computer Architecture and Power-Aware Systems (CAPS) research group at the State University of New York at Binghamton, in addition to hundreds of major universities, industry research labs and several well known microprocessor vendors.

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