socsvn commit: r239377 - soc2012/rudot/sys/kern

[rudot at FreeBSD.org]

Author: rudot
Date: Sat Jul 14 13:00:12 2012
New Revision: 239377
URL: http://svnweb.FreeBSD.org/socsvn/?view=rev&rev=239377

Log:
  supporting both schedulers - fixing %cpu calculations

Modified:
  soc2012/rudot/sys/kern/kern_racct.c

Modified: soc2012/rudot/sys/kern/kern_racct.c
==============================================================================
--- soc2012/rudot/sys/kern/kern_racct.c	Sat Jul 14 12:15:20 2012	(r239376)
+++ soc2012/rudot/sys/kern/kern_racct.c	Sat Jul 14 13:00:12 2012	(r239377)
@@ -145,10 +145,13 @@
 		RACCT_IN_MILLIONS,
 	[RACCT_PCTCPU] = RACCT_RECLAIMABLE | RACCT_DENIABLE };
 
+#ifdef SCHED_4BSD
 /*
  * Contains intermediate values for %cpu calculations to avoid using floating
  * point in the kernel.
- * ccpu_exp[k] = FSCALE * exp(-k/20)
+ * ccpu_exp[k] = FSCALE * (ccpu/FSCALE)^k = FSCALE * exp(-k/20)
+ * It is needed only for the 4BSD scheduler, because in ULE, the ccpu equals to
+ * zero so the calculations are more straightforward.
  */
 fixpt_t ccpu_exp[] = {
 	[0] = FSCALE * 1,
@@ -263,9 +266,18 @@
 	[109] = FSCALE * 0.00429630469075234057,
 	[110] = FSCALE * 0.00408677143846406699,
 };
+#endif
 
 #define	CCPU_EXP_MAX	110
 
+/*
+ * This function is analogical to the getpcpu() function in the ps(1) command.
+ * They should both calculate in the same way so that the racct %cpu
+ * calculations are consistent with the values showed by the ps(1) tool.
+ * The calculations are more complex in the 4BSD scheduler because of the value
+ * of the ccpu variable. In ULE it is defined to be zero which saves us some
+ * work.
+ */
 u_int
 racct_getpcpu(struct proc *p)
 {
@@ -290,14 +302,22 @@
 		pctcpu_next += sched_pctcpu_delta(td);
 		p_pctcpu += max(pctcpu, pctcpu_next);
 #else
+		/*
+		 * In ULE the %cpu statistics are updated on every
+		 * sched_pctcpu() call. So special calculations to
+		 * account for the latest (unfinished) second are
+		 * not needed.
+		 */
 		p_pctcpu += sched_pctcpu(td);
 #endif
 		thread_unlock(td);
 	}
 
+#ifdef SCHED_4BSD
 	if (swtime <= CCPU_EXP_MAX) {
 		return ((100 * p_pctcpu) / (FSCALE - ccpu_exp[swtime]));
 	}
+#endif
 
 	return ((100 * p_pctcpu) / FSCALE);
 }