X-Git-Url: https://git.subgeniuskitty.com/unix-history/.git/blobdiff_plain/da7c5cc62d0962b5d290c48159695646218b130b..6a79e262ebff67defcc88ba77f6eea5894a6b695:/usr/src/sys/kern/kern_synch.c

diff --git a/usr/src/sys/kern/kern_synch.c b/usr/src/sys/kern/kern_synch.c
index 43d7e6f3fe..d6110aa59a 100644
--- a/usr/src/sys/kern/kern_synch.c
+++ b/usr/src/sys/kern/kern_synch.c
@@ -1,27 +1,24 @@
 /*
- * Copyright (c) 1982 Regents of the University of California.
+ * Copyright (c) 1982, 1986 Regents of the University of California.
  * All rights reserved.  The Berkeley software License Agreement
  * specifies the terms and conditions for redistribution.
  *
- *	@(#)kern_synch.c	6.10 (Berkeley) %G%
+ *	@(#)kern_synch.c	7.6 (Berkeley) %G%
  */
 
 #include "../machine/pte.h"
+#include "../machine/psl.h"
+#include "../machine/mtpr.h"
 
 #include "param.h"
 #include "systm.h"
 #include "dir.h"
 #include "user.h"
 #include "proc.h"
-#include "file.h"
-#include "inode.h"
 #include "vm.h"
 #include "kernel.h"
 #include "buf.h"
 
-#ifdef vax
-#include "../vax/mtpr.h"	/* XXX */
-#endif
 /*
  * Force switch among equal priority processes every 100ms.
  */
@@ -33,7 +30,69 @@ roundrobin()
 	timeout(roundrobin, (caddr_t)0, hz / 10);
 }
 
-/* fraction for digital decay to forget 90% of usage in 5*loadav sec */
+/*
+ * constants for digital decay and forget
+ *	90% of (p_cpu) usage in 5*loadav time
+ *	95% of (p_pctcpu) usage in 60 seconds (load insensitive)
+ *          Note that, as ps(1) mentions, this can let percentages
+ *          total over 100% (I've seen 137.9% for 3 processes).
+ *
+ * Note that hardclock updates p_cpu and p_cpticks independently.
+ *
+ * We wish to decay away 90% of p_cpu in (5 * loadavg) seconds.
+ * That is, the system wants to compute a value of decay such
+ * that the following for loop:
+ * 	for (i = 0; i < (5 * loadavg); i++)
+ * 		p_cpu *= decay;
+ * will compute
+ * 	p_cpu *= 0.1;
+ * for all values of loadavg:
+ *
+ * Mathematically this loop can be expressed by saying:
+ * 	decay ** (5 * loadavg) ~= .1
+ *
+ * The system computes decay as:
+ * 	decay = (2 * loadavg) / (2 * loadavg + 1)
+ *
+ * We wish to prove that the system's computation of decay
+ * will always fulfill the equation:
+ * 	decay ** (5 * loadavg) ~= .1
+ *
+ * If we compute b as:
+ * 	b = 2 * loadavg
+ * then
+ * 	decay = b / (b + 1)
+ *
+ * We now need to prove two things:
+ *	1) Given factor ** (5 * loadavg) ~= .1, prove factor == b/(b+1)
+ *	2) Given b/(b+1) ** power ~= .1, prove power == (5 * loadavg)
+ *	
+ * Facts:
+ *         For x close to zero, exp(x) =~ 1 + x, since
+ *              exp(x) = 0! + x**1/1! + x**2/2! + ... .
+ *              therefore exp(-1/b) =~ 1 - (1/b) = (b-1)/b.
+ *         For x close to zero, ln(1+x) =~ x, since
+ *              ln(1+x) = x - x**2/2 + x**3/3 - ...     -1 < x < 1
+ *              therefore ln(b/(b+1)) = ln(1 - 1/(b+1)) =~ -1/(b+1).
+ *         ln(.1) =~ -2.30
+ *
+ * Proof of (1):
+ *    Solve (factor)**(power) =~ .1 given power (5*loadav):
+ *	solving for factor,
+ *      ln(factor) =~ (-2.30/5*loadav), or
+ *      factor =~ exp(-1/((5/2.30)*loadav) =~ exp(-1/(2*loadav)) =
+ *          exp(-1/b) =~ (b-1)/b =~ b/(b+1).                    QED
+ *
+ * Proof of (2):
+ *    Solve (factor)**(power) =~ .1 given factor == (b/(b+1)):
+ *	solving for power,
+ *      power*ln(b/(b+1)) =~ -2.30, or
+ *      power =~ 2.3 * (b + 1) = 4.6*loadav + 2.3 =~ 5*loadav.  QED
+ *
+ * Actual power values for the implemented algorithm are as follows:
+ *      loadav: 1       2       3       4
+ *      power:  5.68    10.32   14.94   19.55
+ */
 #define	filter(loadav) ((2 * (loadav)) / (2 * (loadav) + 1))
 
 double	ccpu = 0.95122942450071400909;		/* exp(-1/20) */
@@ -112,6 +171,7 @@ updatepri(p)
 	p->p_slptime--;		/* the first time was done in schedcpu */
 	while (a && --p->p_slptime)
 		a = (int) (scale * a) /* + p->p_nice */;
+	p->p_slptime = 0;
 	if (a < 0)
 		a = 0;
 	if (a > 255)
@@ -145,15 +205,16 @@ sleep(chan, pri)
 	register struct proc *rp;
 	register struct slpque *qp;
 	register s;
+	extern int cold;
 
 	rp = u.u_procp;
 	s = splhigh();
-	if (panicstr) {
+	if (cold || panicstr) {
 		/*
-		 * After a panic, just give interrupts a chance,
-		 * then just return; don't run any other procs 
-		 * or panic below, in case this is the idle process
-		 * and already asleep.
+		 * After a panic, or during autoconfiguration,
+		 * just give interrupts a chance, then just return;
+		 * don't run any other procs or panic below,
+		 * in case this is the idle process and already asleep.
 		 * The splnet should be spl0 if the network was being used
 		 * by the filesystem, but for now avoid network interrupts
 		 * that might cause another panic.
@@ -262,7 +323,6 @@ restart:
 				/* OPTIMIZED INLINE EXPANSION OF setrun(p) */
 				if (p->p_slptime > 1)
 					updatepri(p);
-				p->p_slptime = 0;
 				p->p_stat = SRUN;
 				if (p->p_flag & SLOAD)
 					setrq(p);
@@ -282,7 +342,6 @@ restart:
 				/* END INLINE EXPANSION */
 				goto restart;
 			}
-			p->p_slptime = 0;
 		} else
 			q = &p->p_link;
 	}
@@ -328,12 +387,12 @@ setrun(p)
 	case SIDL:
 		break;
 	}
-	if (p->p_slptime > 1)
-		updatepri(p);
 	p->p_stat = SRUN;
 	if (p->p_flag & SLOAD)
 		setrq(p);
 	splx(s);
+	if (p->p_slptime > 1)
+		updatepri(p);
 	if (p->p_pri < curpri) {
 		runrun++;
 		aston();