Add the waitx system call to update the creation time, end time and total run time of a process.
Add the ps user command, which, given a process ID, shows information about it such as PID, priority, state, runtime, wait time, times run, current queue, etc.
Add schedulers which can be set using the SCHEDULER flag.
Add RR (default), FCFS, PBS with functions to change the priority of a process, and MLFQ with the ability to change priority and promote or demote a process to 5 different queues accordingly.
The waitx system call modifies defs.h, syscall.c, syscall.h, sysproc.c,
user.h and usys.S to add the system call.
The waitx function is added in proc.c to execute the waitx system call
using the time.c file. This file sends 2 pointers to the waitx call to
store wait time and run time and displays.
In proc.h we added ctime, etime, iotime and rtime to store start time,
end time, I/O time and run time of the file. In allocproc function in
proc.c we set the initial values of these fields. In proc.c these
values are updated and used to calculate the wait and run time.
The ps system call was added similarly to waitx. It is a void function
taking no values but for MLFQ it displays additional fields. It simply
accesses the fields of all the processes and displays them by looping
over the process table. It is implemented in ps.c.
It is implemented like waitx and ps to create a system call from the
set_priority.c file. It searches for the process whose pid matches
the one entered and makes the needed changes. In allocproc() the
default priority for all processes is set to 60.
The schedulers are implemented in proc.c and trap.c mainly.
This is the default policy used, no changes made here.
The start time of each process is checked and once the process with
lowest time is found it is executed. It does not yield in the trap.c
file to ensure FCFS is followed.
A new field priority is added in proc struct. The process with the
highest priority is found after looping through the ptable and is
executed. If it is not the only one, it yields and another process
with equal or higher priority takes its place because of the yield
function and round robin scheduler.
We create an array of queues where all processes are stored. We add the fields queue, ticks, enter, change to implement MLFQ.
Whenever a process exceeds the time in qticks, it is removed from the
present queue and sent to a lower queue, unless it is the lowest queue.
However, if it has been there for more than 30 ticks, it is removed and
sent to a higher queue. Addq and remq add and remove a process from the
queue specified. Incr increases the clock ticks and changeq reassigns the
The userinit, fork, kill, wakeup1, yield, wait, waitx functions are changed
as well to ensure MLFQ executes correctly. In trap.c we check if a process
exceeds its time slice to cause it to yield.'
Analyze the difference between the different schedulers and use a benchmark function to determine which one is fastest.
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".