add system time measurement

src/main.c

@@ -13,9 +13,13 @@ struct RunQ *runq;
 struct PhysPage *first_free_page;
 struct PhysPage *first_busy_page;
 
+size_t system_time;
+
 int
 main(void)
 {
+	system_time = 0;
+
 	first_busy_page = NULL;
 	
 	first_free_page = malloc(sizeof(struct PhysPage));

src/mmu.c

@@ -2,6 +2,10 @@
 
 #include "kernel.h"
 
+
+extern size_t system_time;
+
+
 void MMU_read(struct PageTableEntry *pt, size_t page_no)
 {
 	if (!pt[page_no].p)
@@ -9,6 +13,8 @@ void MMU_read(struct PageTableEntry *pt, size_t page_no)
 
 	printf("[mmu:read] pt[%d] -> ppn %d\n", page_no, pt[page_no].ppn);
 	pt[page_no].r = 1;
+
+	system_time++;
 }
 
 void MMU_write(struct PageTableEntry *pt, size_t page_no)
@@ -19,4 +25,6 @@ void MMU_write(struct PageTableEntry *pt, size_t page_no)
 	printf("[mmu:write] pt[%d] -> ppn %d\n", page_no, pt[page_no].ppn);
 	pt[page_no].r = 1;
 	pt[page_no].m = 1;
+
+	system_time++;
 }