This implementation adds threads and thread management to XV6 operating system at a higher level. Microcode implementation of XV6 is not changed since it's hardware specific and it's not designed to work with multi core CPUs. Threads added work in a time sharing manner and in order to manage them multiple scheduling algorithms are realized.
The main challenges with multi treading include:
- Resource allocation, sharing and deallocation between threads of the same process
- Thread Identification
- Joining to a specific thread of a specific process and returning its results
Following scheduling algorithms have been realized:
- Round-Robin
- Preemptive Priority Scheduling
- Preemptive Multilevel Queue Scheduling
- Lottery Scheduling
In order to assess performance of the overall system and each of the scheduling algorithms some metrics and tests had to be added to the system. For each of the scheduling algorithms one test has been implemented with respect its function. Since the base operating system and every test program runs using a unified scheduling algorithm in order to run a specific test program with a specific scheduling algorithm, a system-call named changePolicy has been added in order to change the scheduling algorithm while the operating system is functional and this has been done with no down-time. In order to measure algorithm performance the following variables have been added to process statistics:
- CPU Burst Time
- Turnaround Time
- Waiting Time
NOTE: we have stopped maintaining the x86 version of xv6, and switched our efforts to the RISC-V version (https://github.com/mit-pdos/xv6-riscv.git)
xv6 is a re-implementation of Dennis Ritchie's and Ken Thompson's Unix Version 6 (v6). xv6 loosely follows the structure and style of v6, but is implemented for a modern x86-based multiprocessor using ANSI C.
ACKNOWLEDGMENTS
xv6 is inspired by John Lions's Commentary on UNIX 6th Edition (Peer to Peer Communications; ISBN: 1-57398-013-7; 1st edition (June 14, 2000)). See also https://pdos.csail.mit.edu/6.828/, which provides pointers to on-line resources for v6.
xv6 borrows code from the following sources: JOS (asm.h, elf.h, mmu.h, bootasm.S, ide.c, console.c, and others) Plan 9 (entryother.S, mp.h, mp.c, lapic.c) FreeBSD (ioapic.c) NetBSD (console.c)
The following people have made contributions: Russ Cox (context switching, locking), Cliff Frey (MP), Xiao Yu (MP), Nickolai Zeldovich, and Austin Clements.
We are also grateful for the bug reports and patches contributed by Silas Boyd-Wickizer, Anton Burtsev, Cody Cutler, Mike CAT, Tej Chajed, eyalz800, Nelson Elhage, Saar Ettinger, Alice Ferrazzi, Nathaniel Filardo, Peter Froehlich, Yakir Goaron,Shivam Handa, Bryan Henry, Jim Huang, Alexander Kapshuk, Anders Kaseorg, kehao95, Wolfgang Keller, Eddie Kohler, Austin Liew, Imbar Marinescu, Yandong Mao, Matan Shabtay, Hitoshi Mitake, Carmi Merimovich, Mark Morrissey, mtasm, Joel Nider, Greg Price, Ayan Shafqat, Eldar Sehayek, Yongming Shen, Cam Tenny, tyfkda, Rafael Ubal, Warren Toomey, Stephen Tu, Pablo Ventura, Xi Wang, Keiichi Watanabe, Nicolas Wolovick, wxdao, Grant Wu, Jindong Zhang, Icenowy Zheng, and Zou Chang Wei.
The code in the files that constitute xv6 is Copyright 2006-2018 Frans Kaashoek, Robert Morris, and Russ Cox.
ERROR REPORTS
We don't process error reports (see note on top of this file).
BUILDING AND RUNNING XV6
To build xv6 on an x86 ELF machine (like Linux or FreeBSD), run "make". On non-x86 or non-ELF machines (like OS X, even on x86), you will need to install a cross-compiler gcc suite capable of producing x86 ELF binaries (see https://pdos.csail.mit.edu/6.828/). Then run "make TOOLPREFIX=i386-jos-elf-". Now install the QEMU PC simulator and run "make qemu".