First cut at lottery scheduler assignment.

scheduling-xv6-lottery/README.md

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+# An xv6 Lottery Scheduler
+
+In this project, you'll be putting a new scheduler into xv6. It is called a
+**lottery scheduler**, and the full version is described in [this
+chapter](a,href=http://www.cs.wisc.edu/~remzi/OSFEP/cpu-sched-lottery.pdf) of
+the online book; you'll be building a simpler one.  The basic idea is simple:
+assign each running process a slice of the processor based in proportion to
+the number of tickets it has; the more tickets a process has, the more it
+runs. Each time slice, a randomized lottery determines the winner of the
+lottery; that winning process is the one that runs for that time slice.
+
+The objectives for this project:
+* To gain further knowledge of a real kernel, xv6.
+* To familiarize yourself with a scheduler.
+* To change that scheduler to a new algorithm.
+* To make a graph to show your project behaves appropriately.
+
+
+## Details
+
+You'll need two new system calls to implement this scheduler. The first is
+`int settickets(int number)`, which sets the number of tickets of the calling
+process. By default, each process should get one ticket; calling this routine
+makes it such that a process can raise the number of tickets it receives, and
+thus receive a higher proportion of CPU cycles. This routine should return 0
+if successful, and -1 otherwise (if, for example, the caller passes in a
+number less than one).
+
+The second is `int getpinfo(struct pstat *)`. This routine returns some
+information about all running processes, including how many times each has
+been chosen to run and the process ID of each. You can use this system call to
+build a variant of the command line program `ps`, which can then be called to
+see what is going on. The structure `pstat` is defined below.
+
+Most of the code for the scheduler is quite localized and can be found in
+`proc.c`; the associated header file, `proc.h` is also quite useful to
+examine. To change the scheduler, not much needs to be done; study its control
+flow and then try some small changes. 
+
+You'll also need to figure out how to generate random numbers in the kernel;
+some searching should lead you to a simple pseudo-random number generator,
+which you can then include in the kernel and use as appropriate.
+
+Finally, you'll need to understand how to fill in the structure `pstat` in the
+kernel and pass the results to user space. The structure should look like what
+you see here, in a file you'll have to include called `pstat.h`:
+
+```c
+#ifndef _PSTAT_H_
+#define _PSTAT_H_
+
+#include "param.h"
+
+struct pstat {
+  int inuse[NPROC];   // whether this slot of the process table is in use (1 or 0)
+  int tickets[NPROC]; // the number of tickets this process has
+  int pid[NPROC];     // the PID of each process 
+  int ticks[NPROC];   // the number of ticks each process has accumulated 
+};
+
+#endif // _PSTAT_H_
+```
+
+## Graph
+
+Beyond the usual code, you'll have to make a graph for this assignment. The
+graph should show the number of time slices a set of three processes receives
+over time, where the processes have a 3:2:1 ratio of tickets (e.g., process A
+might have 30 tickets, process B 20, and process C 10). The graph is likely to
+be pretty boring, but should clearly show that your lottery scheduler works as
+desired.
+
+
+
+
+