Simics : A Full System Simulation Platform

Simics: A Full System Simulation Platform Peter S. Magnusson, Magnus Crhistensson, Jesper Eskilson, Daniel Forsgren, Gustav Hallberg, Johan Högberg, Frederik larsson, Anreas Moestedt. Presented by Eduardo Cuervo

Theproblem… • Simulation is an important step • Research • Evaluation • Computer Design • Not enough to simulate only user level code • Not accurate enough • Need for Full System Simulation (slower) • Simulation must be able to interface with detailed HW models timely.

Simulationtaxonomy • Scope (What is modeled?) • Full system • User level • Level of abstraction • Functional behavior (what) • Timing behavior (when) • Realistic workloads • Functional:Boot, run unmodified OS, benchmarks • Timing: Support hardware engineering • Fast enough to run real workloads

Simics • Full systemsimulator • Instruction-set level • Supportformultiplearchitectures • SPARC • Alpha • X86 • Itanium • MIPS • ARM • Unmodified OS support

Simics • Processor Models • Device Models • Accurate enough for real drivers and firmware • Simics Central • Creation of full-scale distributed system • Router • Communicates multiple Simics instances • Multiple nodes of the same architecture per instance • Synchronizesinstances

Applications • Microprocessor design • Interaction with memory manager an scheduler • Approximate cache and I/O timing models • Scalable to full server workloads (TPC-C) • OoO Support, custom ROB but no pipeline • Memory studies • Memory Spaces  Address Spaces • Extendable with timing models • OS Development • Implementation of very specific breakpoints • Debugging

Implementation • Simics Central • Synchronizes virtual time • Simulation speed = speed of the slowest Simics process • Configuration • Object Oriented • Command Line Interface (CLI) and Scripting • Built-in Python runtime environment • Scripts tied to events (TLB misses, I/O operations) • Devices • Timer, floppy, keyboard,mouse, DMA,interrupt,etc.

Simics Central

Simics Configuration OBJECT cpu0 TYPE x86-hammer { freq_mhz: 3500 physical_memory: phys_mem0 } OBJECT phys_mem0 TYPE memory-space { map: ((0xa0000, vga0, 1, 0, 0x20000), (0x100000, mem0, 0, 0x100000, 0xff00000), ... } OBJECT con0 TYPE gfx-console { queue: cpu0 x-size: 720 y-size: 400 keyboard: kbd0 Mouse: kbd0 }

Scripting Example from sim_core import * import conf def break_handler(id): if conf.cpu0.eax > conf.cpu0.ecx: raise SimExc_Break id = SIM_breakpoint(conf.phys_mem0, Break_Physical, Break_Execute, 0x000f2501, 1, 0) SIM_hap_register_callback( “Core_Breakpoint” ,break_handler, id)

Implementation • HDL interface • Link Simics to Verilog through C interface • Simics API • Makes Simics extensible • Write new device models, commands, routines • Memory • Biggest performance challenge • Simulator transaction cache

Simulator transaction cache • Speeds up loads, stores and fetches • Pointers to simulated memory • Indexed by virtual address • No side effects on hit • Alignment exception, TLB miss, cache miss, breakpoint • Interpreter cache • Hit inlined in the kernel • Most complex construct

Event Handling • Two event queues • Step queue • Triggered by program counter steps • Time queue • Resolution of a processor clock cycle • Mix of time-driven and event-driven components

Threaded Code Interpreter • Specification language: Sim Gen • Generates all permitted combinations • Better interpreter than practical to do manually • Outputs an interpreter in C // IA32/x86-64 add to left instruction instruction ADD_L({REG}, {REG_OR_MEM}) pattern op_h2 == 0 && opl == 0 && d == 1 && opm == 0 syntax “add {REG},{REG_OR_MEM}” semantics #{ ireg_t op1 = {REG}; ireg_t op2 = {REG_OR_MEM}; ireg_t dst = op1 + op2; EFLAGS_ADD(dst,op1,op2,w,os); SET({REG_W}, dst); #} attributes type = IT_ALU

SimGen

Simics Architecture

Performance • Os boot workloads • Modeled with 7 processor architectures • Scalability shown on Ultra II Enterprise Servers • Increasing number of CPUs • Lower performance on OoO versions

Performance

Related Work • IBM first emulator (7070) • PDP-11 • G88 • Gsim • Based on g88 • Rewritten as the first version of simics • SimOS • MIPS-based processor • Similar goals and solutions • More general solution • Three CPU simulators

Conclusion • Full system simulation is required for realistic workloads • Simics offers a valuable simulation tool for designing and evaluating HW • Support for scripting, networking, and multiple architectures are a great advantage

Simics : A Full System Simulation Platform