Hi!

> > I've got one question about how the cpu consumption is calculated.
> > 
> > Bellow are two programs that do the same thing, play stuff to the soundcard.
> > The first uses a blocking write, the second a nonblocking one with a select.
> > The select does not block (if it did, the cpu consumption is reported to
> > be the same than the first method, both by ps and top). It does an
> > usleep(10*1000) if there is no space left in the audio buffers.
> > 
> > My question is : why does the first get 5% of cpu consumption reported
> > by both ps and top when the second gets only 0.1% ? They both do the same
> > calculations, so it should be equal, nope ? Is it related to the kernel
> > or just the ps and top programs ? (Is it only a problem ?)
> 
> Kernel cpu meters do not work too well, see may badboy examples and
> discussion around them. I even have patch, somewhere... Search archives.

Following up myself, anyway, here's the patch. Tell me if it makes a
difference.
									Pavel

--- clean/kernel/sched.c	Fri Mar 26 17:46:31 1999
+++ linux/kernel/sched.c	Fri Mar 26 17:31:12 1999
@@ -78,6 +78,7 @@
 long time_adjust = 0;
 long time_adjust_step = 0;
 
+int need_update_times = 0;
 unsigned long event = 0;
 
 extern int do_setitimer(int, struct itimerval *, struct itimerval *);
@@ -98,6 +99,8 @@
 
 struct kernel_stat kstat = { 0 };
 
+static void update_process_times(struct task_struct *p, unsigned long ticks, unsigned long system);
+
 void scheduling_functions_start_here(void) { }
 
 #ifdef __SMP__
@@ -767,17 +772,22 @@
  	next->has_cpu = 1;
 	spin_unlock(&scheduler_lock);
 #endif /* __SMP__ */
- 	if (prev != next) {
+
+	if (need_update_times)
+		update_process_times( next, 1, 1 );
+
+	if (prev != next) {
 #ifdef __SMP__
 		sched_data->prev = prev;
 #endif
-	 	kstat.context_swtch++;
+		kstat.context_swtch++;
+
 		get_mmu_context(next);
 		switch_to(prev,next);
 
 		__schedule_tail();
 	}
-  
+
 	reacquire_kernel_lock(current);
 	return;
 
@@ -1357,14 +1367,15 @@
 	do_it_prof(p, ticks);
 }	
 
-static void update_process_times(unsigned long ticks, unsigned long system)
+static void update_process_times(struct task_struct *p, unsigned long ticks, unsigned long system)
 {
 /*
  * SMP does this on a per-CPU basis elsewhere
  */
 #ifndef  __SMP__
-	struct task_struct * p = current;
 	unsigned long user = ticks - system;
+	need_update_times = 0;
+
 	if (p->pid) {
 		p->counter -= ticks;
 		if (p->counter < 0) {
@@ -1410,8 +1421,11 @@
 		calc_load(ticks);
 		update_wall_time(ticks);
 		write_unlock_irq(&xtime_lock);
-		
-		update_process_times(ticks, system);
+
+		if (current->pid || (!current->need_resched))
+			update_process_times(current, ticks, system);
+		else
+			need_update_times = 1;
 
 	} else
 		write_unlock_irq(&xtime_lock);
@@ -1419,20 +1433,20 @@
 
 static void timer_bh(void)
 {
-	update_times();
 	run_old_timers();
 	run_timer_list();
+	update_times();
 }
 
 void do_timer(struct pt_regs * regs)
 {
-	(*(unsigned long *)&jiffies)++;
+	(*(unsigned long *)&jiffies)++; /* Otherwise gcc will generate ugly code */
 	lost_ticks++;
-	mark_bh(TIMER_BH);
 	if (!user_mode(regs))
 		lost_ticks_system++;
 	if (tq_timer)
 		mark_bh(TQUEUE_BH);
+	mark_bh(TIMER_BH);
 }
 
 #ifndef __alpha__

-- 
I'm really pavel@ucw.cz. Look at http://195.113.31.123/~pavel.          Pavel
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