From: cheloha <cheloha@openbsd.org>
Date: Sun, 4 Dec 2022 18:01:57 +0000 (+0000)
Subject: systat(1): vmstat: measure elapsed time with clock_gettime(2) instead of ticks
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=be5c9bf8edd6e653dc889b59d54f26a9013a6965;p=openbsd

systat(1): vmstat: measure elapsed time with clock_gettime(2) instead of ticks

The vmstat view in systat(1) should not use statclock() ticks to count
elapsed time.  First, ticks are low resolution.  Second, the statclock
is sometimes randomized, so each tick is not necessarily of equal
length.  Third, we're counting ticks from every CPU on the system, so
every rate in the view is divided by the number of CPUs.  For example,
on an amd64 system with 8 CPUs you currently see:

     200 clock

... when the true clock interrupt rate on that system is 1600.

Instead, measure elapsed time with clock_gettime(2).  Use CLOCK_UPTIME
here so we exclude time when the system is suspended.  With this
change we no longer need "stathz" or "hertz".  We can also get rid of
the anachronistic secondary clock failure test.

Prompted by dlg@ and jmatthew@.  deraadt@ says this has been in snaps
since 2022-11-21; no complaints.

Link: https://marc.info/?l=openbsd-tech&m=166898960831136&w=2

ok dlg@ deraadt@
---

diff --git a/usr.bin/systat/main.c b/usr.bin/systat/main.c
index 7a4225cc490..ce7851d8bd2 100644
--- a/usr.bin/systat/main.c
+++ b/usr.bin/systat/main.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: main.c,v 1.76 2021/07/12 15:09:20 beck Exp $	 */
+/* $OpenBSD: main.c,v 1.77 2022/12/04 18:01:57 cheloha Exp $	 */
 /*
  * Copyright (c) 2001, 2007 Can Erkin Acar
  * Copyright (c) 2001 Daniel Hartmeier
@@ -65,7 +65,7 @@ double	avenrun[3];
 double	naptime = 5.0;
 int	verbose = 1;		/* to report kvm read errs */
 int	nflag = 1;
-int	ut, hz, stathz;
+int	ut, hz;
 char    hostname[HOST_NAME_MAX+1];
 WINDOW  *wnd;
 int	CMDLINE;
@@ -414,7 +414,6 @@ gethz(void)
 	mib[1] = KERN_CLOCKRATE;
 	if (sysctl(mib, 2, &cinf, &size, NULL, 0) == -1)
 		return;
-	stathz = cinf.stathz;
 	hz = cinf.hz;
 }
 
diff --git a/usr.bin/systat/systat.h b/usr.bin/systat/systat.h
index e7d20070541..776be5a2d51 100644
--- a/usr.bin/systat/systat.h
+++ b/usr.bin/systat/systat.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: systat.h,v 1.24 2021/01/18 00:49:09 mortimer Exp $	*/
+/*	$OpenBSD: systat.h,v 1.25 2022/12/04 18:01:57 cheloha Exp $	*/
 /*	$NetBSD: systat.h,v 1.2 1995/01/20 08:52:14 jtc Exp $	*/
 
 /*-
@@ -58,7 +58,7 @@ extern kvm_t	*kd;
 extern long	ntext;
 extern int	*dk_select;
 extern int	dk_ndrive;
-extern int	hz, stathz;
+extern int	hz;
 extern double	naptime;
 extern size_t	nhosts;
 extern size_t	nports;
diff --git a/usr.bin/systat/vmstat.c b/usr.bin/systat/vmstat.c
index ce22f73d9c8..9cb43279199 100644
--- a/usr.bin/systat/vmstat.c
+++ b/usr.bin/systat/vmstat.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: vmstat.c,v 1.94 2022/02/22 17:35:01 deraadt Exp $	*/
+/*	$OpenBSD: vmstat.c,v 1.95 2022/12/04 18:01:57 cheloha Exp $	*/
 /*	$NetBSD: vmstat.c,v 1.5 1996/05/10 23:16:40 thorpej Exp $	*/
 
 /*-
@@ -98,7 +98,6 @@ int select_vm(void);
 int vm_keyboard_callback(int);
 
 static	time_t t;
-static	float hertz;
 static	int nintr;
 static	long *intrloc;
 static	char **intrname;
@@ -170,7 +169,6 @@ initvmstat(void)
 	int mib[4], i;
 	size_t size;
 
-	hertz = stathz;
 	if (!dkinit(1))
 		return(0);
 
@@ -323,7 +321,6 @@ labelkre(void)
 		Y(fld); \
 		putint((int)((float)s.fld/etime + 0.5), l, c, w); \
 	} while (0)
-#define MAXFAIL 5
 
 static	char cpuchar[] = { '|', '@', '=', '>', ' ' };
 static	char cpuorder[] = { CP_INTR, CP_SPIN, CP_SYS, CP_USER, CP_IDLE };
@@ -331,33 +328,27 @@ static	char cpuorder[] = { CP_INTR, CP_SPIN, CP_SYS, CP_USER, CP_IDLE };
 void
 showkre(void)
 {
+	static struct timespec prev;
+	struct timespec elapsed, now;
 	float f1, f2;
 	int psiz;
 	u_int64_t inttotal, intcnt;
 	int i, l, c;
-	static int failcnt = 0, first_run = 0;
+	static int first_run = 0;
 	double etime;
 
+	clock_gettime(CLOCK_UPTIME, &now);
+	timespecsub(&now, &prev, &elapsed);
+	prev = now;
 	if (state == TIME) {
 		if (!first_run) {
 			first_run = 1;
 			return;
 		}
 	}
-	etime = 0;
-	for (i = 0; i < CPUSTATES; i++) {
+	etime = elapsed.tv_sec + elapsed.tv_nsec / 1000000000.0;
+	for (i = 0; i < CPUSTATES; i++)
 		X(cpustats.cs_time);
-		etime += s.cpustats.cs_time[i];
-	}
-	if (etime < 5.0) {	/* < 5 ticks - ignore this trash */
-		if (failcnt++ >= MAXFAIL) {
-			error("The alternate system clock has died!");
-			failcnt = 0;
-		}
-		return;
-	}
-	failcnt = 0;
-	etime /= hertz;
 	inttotal = 0;
 	for (i = 0; i < nintr; i++) {
 		t = intcnt = s.intrcnt[i];