Lottery scheduling code

README.md

@@ -11,7 +11,7 @@ CPU Virtualization Chapters:
 * Direct Execution
 * CPU Scheduling
 * Multi-level Feedback
-* Lottery Scheduling
+* [Lottery Scheduling](https://github.com/remzi-arpacidusseau/ostep-code/tree/master/cpu-sched-lottery)
 * Multi-CPU Scheduling
 
 Memory Virtualization Chapters:

cpu-sched-lottery/README.md

@@ -0,0 +1,21 @@
+
+## Proportional Share Scheduling
+
+Code from OSTEP chapter [Scheduling: Proportional Share](http://pages.cs.wisc.edu/~remzi/OSTEP/cpu-sched-lottery.pdf).
+
+Compile with:
+
+```
+prompt> gcc -o lottery lottery.c -Wall
+```
+
+Run like this:
+
+```
+./lottery 1 100
+```
+
+which uses random seed '1' to run a little lottery 100 different times.
+
+Read the source code for details.
+

cpu-sched-lottery/lottery.c

@@ -0,0 +1,74 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+
+// global ticket count
+int gtickets = 0;
+
+struct node_t {
+    int            tickets;
+    struct node_t *next;
+};
+
+struct node_t *head = NULL;
+
+void insert(int tickets) {
+    struct node_t *tmp = malloc(sizeof(struct node_t));
+    assert(tmp != NULL);
+    tmp->tickets = tickets;
+    tmp->next    = head;
+    head         = tmp;
+    gtickets    += tickets;
+}
+
+void print_list() {
+    struct node_t *curr = head;
+    printf("List: ");
+    while (curr) {
+	printf("[%d] ", curr->tickets);
+	curr = curr->next;
+    }
+    printf("\n");
+}
+
+int
+main(int argc, char *argv[])
+{
+    if (argc != 3) {
+	fprintf(stderr, "usage: lottery <seed> <loops>\n");
+	exit(1);
+    }
+    int seed  = atoi(argv[1]);
+    int loops = atoi(argv[2]);
+    srandom(seed);
+
+    // populate list with some number of jobs, each
+    // with some number of tickets
+    insert(50);
+    insert(100);
+    insert(25);
+
+    print_list();
+    
+    int i;
+    for (i = 0; i < loops; i++) {
+	int counter            = 0;
+	int winner             = random() % gtickets; // get winner
+	struct node_t *current = head;
+
+	// loop until the sum of ticket values is > the winner
+	while (current) {
+	    counter = counter + current->tickets;
+	    if (counter > winner)
+		break; // found the winner
+	    current = current->next;
+	}
+	// current is the winner: schedule it...
+	print_list();
+	printf("winner: %d %d\n\n", winner, current->tickets);
+
+    }
+    return 0;
+}
+