PATCH: per user fair scheduler 2.4.19 (cleaned up, thanks hch) (was: Re: Offtopic: (was Re: [ANNOUNCE] Native POSIX Thread Library 0.1))

[Rik van Riel <riel@conectiva.com.br>]

On Tue, 24 Sep 2002, Michael Sinz wrote:
> Rik van Riel wrote:

> > I've got per user scheduling.  I'm currently porting it to 2.4.19
> > (and having fun with some very subtle bugs) and am thinking about
> > how to port this beast to the O(1) scheduler in a clean way.

> I would be interested in seeing this patch.

Here it is again, this version has undergone some cleanups
after complaints by Christoph Hellwig ;)

Rik
-- 
A: No.
Q: Should I include quotations after my reply?

http://www.surriel.com/		http://distro.conectiva.com/


--- linux/kernel/sched.c.fair	2002-09-20 10:58:49.000000000 -0300
+++ linux/kernel/sched.c	2002-09-24 14:46:31.000000000 -0300
@@ -45,31 +45,33 @@

 extern void mem_use(void);

+#ifdef CONFIG_FAIRSCHED
+/* Toggle the per-user fair scheduler on/off */
+int fairsched = 1;
+
+/* Move a task to the tail of the tasklist */
+static inline void move_last_tasklist(struct task_struct * p)
+{
+	/* list_del */
+	p->next_task->prev_task = p->prev_task;
+	p->prev_task->next_task = p->next_task;
+
+	/* list_add_tail */
+	p->next_task = &init_task;
+	p->prev_task = init_task.prev_task;
+	init_task.prev_task->next_task = p;
+	init_task.prev_task = p;
+}
+
 /*
- * Scheduling quanta.
- *
- * NOTE! The unix "nice" value influences how long a process
- * gets. The nice value ranges from -20 to +19, where a -20
- * is a "high-priority" task, and a "+10" is a low-priority
- * task.
- *
- * We want the time-slice to be around 50ms or so, so this
- * calculation depends on the value of HZ.
+ * Remember p->next, in case we call move_last_tasklist(p) in the
+ * fairsched recalculation code.
  */
-#if HZ < 200
-#define TICK_SCALE(x)	((x) >> 2)
-#elif HZ < 400
-#define TICK_SCALE(x)	((x) >> 1)
-#elif HZ < 800
-#define TICK_SCALE(x)	(x)
-#elif HZ < 1600
-#define TICK_SCALE(x)	((x) << 1)
-#else
-#define TICK_SCALE(x)	((x) << 2)
-#endif
-
-#define NICE_TO_TICKS(nice)	(TICK_SCALE(20-(nice))+1)
+#define safe_for_each_task(p) \
+	for (p = init_task.next_task, next = p->next_task ; p != &init_task ; \
+			p = next, next = p->next_task)

+#endif /* CONFIG_FAIRSCHED */

 /*
  *	Init task must be ok at boot for the ix86 as we will check its signals
@@ -460,6 +462,54 @@
 }

 /*
+ * If the remaining timeslice lengths of all runnable tasks reach 0
+ * the scheduler recalculates the priority of all processes.
+ */
+static void recalculate_priorities(void)
+{
+#ifdef CONFIG_FAIRSCHED
+	if (fairsched) {
+		struct task_struct *p, *next;
+		struct user_struct *up;
+		long oldcounter, newcounter;
+
+		recalculate_peruser_cputicks();
+
+		write_lock_irq(&tasklist_lock);
+		safe_for_each_task(p) {
+			up = p->user;
+			if (up->cpu_ticks > 0) {
+				oldcounter = p->counter;
+				newcounter = (oldcounter >> 1) +
+					NICE_TO_TICKS(p->nice);
+				up->cpu_ticks += oldcounter;
+				up->cpu_ticks -= newcounter;
+				/*
+				 * If a user is very busy, only some of its
+				 * processes can get CPU time. We move those
+				 * processes out of the way to prevent
+				 * starvation of others.
+				 */
+				if (oldcounter != newcounter) {
+					p->counter = newcounter;
+					move_last_tasklist(p);
+				}
+			}
+		}
+		write_unlock_irq(&tasklist_lock);
+	} else
+#endif /* CONFIG_FAIRSCHED */
+	{
+		struct task_struct *p;
+
+		read_lock(&tasklist_lock);
+		for_each_task(p)
+			p->counter = (p->counter >> 1) + NICE_TO_TICKS(p->nice);
+		read_unlock(&tasklist_lock);
+	}
+}
+
+/*
  * schedule_tail() is getting called from the fork return path. This
  * cleans up all remaining scheduler things, without impacting the
  * common case.
@@ -616,13 +666,10 @@

 	/* Do we need to re-calculate counters? */
 	if (unlikely(!c)) {
-		struct task_struct *p;
-
 		spin_unlock_irq(&runqueue_lock);
-		read_lock(&tasklist_lock);
-		for_each_task(p)
-			p->counter = (p->counter >> 1) + NICE_TO_TICKS(p->nice);
-		read_unlock(&tasklist_lock);
+
+		recalculate_priorities();
+
 		spin_lock_irq(&runqueue_lock);
 		goto repeat_schedule;
 	}
--- linux/kernel/user.c.fair	2002-09-20 11:50:56.000000000 -0300
+++ linux/kernel/user.c	2002-09-24 16:06:11.000000000 -0300
@@ -29,9 +29,12 @@
 struct user_struct root_user = {
 	__count:	ATOMIC_INIT(1),
 	processes:	ATOMIC_INIT(1),
-	files:		ATOMIC_INIT(0)
+	files:		ATOMIC_INIT(0),
+	cpu_ticks:	NICE_TO_TICKS(0)
 };

+static LIST_HEAD(user_list);
+
 /*
  * These routines must be called with the uidhash spinlock held!
  */
@@ -44,6 +47,8 @@
 		next->pprev = &up->next;
 	up->pprev = hashent;
 	*hashent = up;
+
+	list_add(&up->list, &user_list);
 }

 static inline void uid_hash_remove(struct user_struct *up)
@@ -54,6 +59,8 @@
 	if (next)
 		next->pprev = pprev;
 	*pprev = next;
+
+	list_del(&up->list);
 }

 static inline struct user_struct *uid_hash_find(uid_t uid, struct user_struct **hashent)
@@ -101,6 +108,7 @@
 		atomic_set(&new->__count, 1);
 		atomic_set(&new->processes, 0);
 		atomic_set(&new->files, 0);
+		new->cpu_ticks = NICE_TO_TICKS(0);

 		/*
 		 * Before adding this, check whether we raced
@@ -120,6 +128,21 @@
 	return up;
 }

+/* Fair scheduler, recalculate the per user cpu time cap. */
+void recalculate_peruser_cputicks(void)
+{
+	struct list_head * entry;
+	struct user_struct * user;
+
+	spin_lock(&uidhash_lock);
+	list_for_each(entry, &user_list) {
+		user = list_entry(entry, struct user_struct, list);
+		user->cpu_ticks = (user->cpu_ticks / 2) + NICE_TO_TICKS(0);
+	}
+	/* Needed hack, we can get called before uid_cache_init ... */
+	root_user.cpu_ticks = (root_user.cpu_ticks / 2) + NICE_TO_TICKS(0);
+	spin_unlock(&uidhash_lock);
+}

 static int __init uid_cache_init(void)
 {
--- linux/kernel/sysctl.c.fair	2002-09-21 00:00:36.000000000 -0300
+++ linux/kernel/sysctl.c	2002-09-21 20:40:49.000000000 -0300
@@ -50,6 +50,7 @@
 extern int sysrq_enabled;
 extern int core_uses_pid;
 extern int cad_pid;
+extern int fairsched;

 /* this is needed for the proc_dointvec_minmax for [fs_]overflow UID and GID */
 static int maxolduid = 65535;
@@ -256,6 +257,10 @@
 	{KERN_S390_USER_DEBUG_LOGGING,"userprocess_debug",
 	 &sysctl_userprocess_debug,sizeof(int),0644,NULL,&proc_dointvec},
 #endif
+#ifdef CONFIG_FAIRSCHED
+	{KERN_FAIRSCHED, "fairsched", &fairsched, sizeof(int),
+	 0644, NULL, &proc_dointvec},
+#endif
 	{0}
 };

--- linux/include/linux/sched.h.fair	2002-09-20 10:59:03.000000000 -0300
+++ linux/include/linux/sched.h	2002-09-24 15:12:50.000000000 -0300
@@ -275,6 +275,10 @@
 	/* Hash table maintenance information */
 	struct user_struct *next, **pprev;
 	uid_t uid;
+
+	/* Linked list for for_each_user */
+	struct list_head list;
+	long cpu_ticks;
 };

 #define get_current_user() ({ 				\
@@ -282,6 +286,7 @@
 	atomic_inc(&__user->__count);			\
 	__user; })

+extern void recalculate_peruser_cputicks(void);
 extern struct user_struct root_user;
 #define INIT_USER (&root_user)

@@ -422,6 +427,31 @@
 };

 /*
+ * Scheduling quanta.
+ *
+ * NOTE! The unix "nice" value influences how long a process
+ * gets. The nice value ranges from -20 to +19, where a -20
+ * is a "high-priority" task, and a "+10" is a low-priority
+ * task.
+ *
+ * We want the time-slice to be around 50ms or so, so this
+ * calculation depends on the value of HZ.
+ */
+#if HZ < 200
+#define TICK_SCALE(x)	((x) >> 2)
+#elif HZ < 400
+#define TICK_SCALE(x)	((x) >> 1)
+#elif HZ < 800
+#define TICK_SCALE(x)	(x)
+#elif HZ < 1600
+#define TICK_SCALE(x)	((x) << 1)
+#else
+#define TICK_SCALE(x)	((x) << 2)
+#endif
+
+#define NICE_TO_TICKS(nice)	(TICK_SCALE(20-(nice))+1)
+
+/*
  * Per process flags
  */
 #define PF_ALIGNWARN	0x00000001	/* Print alignment warning msgs */
--- linux/include/linux/sysctl.h.fair	2002-09-21 20:41:18.000000000 -0300
+++ linux/include/linux/sysctl.h	2002-09-21 20:41:43.000000000 -0300
@@ -124,6 +124,7 @@
 	KERN_CORE_USES_PID=52,		/* int: use core or core.%pid */
 	KERN_TAINTED=53,	/* int: various kernel tainted flags */
 	KERN_CADPID=54,		/* int: PID of the process to notify on CAD */
+	KERN_FAIRSCHED=55,	/* int: turn fair scheduler on/off */
 };


--- linux/arch/i386/config.in.fair	2002-09-21 20:42:06.000000000 -0300
+++ linux/arch/i386/config.in	2002-09-21 20:42:35.000000000 -0300
@@ -261,6 +261,9 @@
 bool 'System V IPC' CONFIG_SYSVIPC
 bool 'BSD Process Accounting' CONFIG_BSD_PROCESS_ACCT
 bool 'Sysctl support' CONFIG_SYSCTL
+if [ "$CONFIG_EXPERIMENTAL" = "y" ] ; then
+   bool 'Fair scheduler' CONFIG_FAIRSCHED
+fi
 if [ "$CONFIG_PROC_FS" = "y" ]; then
    choice 'Kernel core (/proc/kcore) format' \
 	"ELF		CONFIG_KCORE_ELF	\
--- linux/arch/alpha/config.in.fair	2002-08-02 21:39:42.000000000 -0300
+++ linux/arch/alpha/config.in	2002-09-21 20:43:21.000000000 -0300
@@ -273,6 +273,9 @@
 bool 'System V IPC' CONFIG_SYSVIPC
 bool 'BSD Process Accounting' CONFIG_BSD_PROCESS_ACCT
 bool 'Sysctl support' CONFIG_SYSCTL
+if [ "$CONFIG_EXPERIMENTAL" = "y" ] ; then
+   bool 'Fair scheduler' CONFIG_FAIRSCHED
+fi
 if [ "$CONFIG_PROC_FS" = "y" ]; then
    choice 'Kernel core (/proc/kcore) format' \
 	"ELF		CONFIG_KCORE_ELF	\