The us/sy/id CPU usage numbers in the first line of vmstat are not useful,
because they're calculated based on kern.cp_times since boot, and not a
delta as are all subsequent lines. If the system has been up long enough
wrapping may come in to play, giving negative results. For example, on
one machine I see:
$ vmstat 1
procs memory page disks faults cpu
r b w avm fre flt re pi po fr sr da0 pa0 in sy cs us sy id
1 0 2 1097M 227M 101 0 0 0 195 45 0 0 483 40 243 -24 -33 157
1 0 2 1102M 222M 1396 0 0 0 0 0 0 0 159 2170 826 25 2 74
1 0 2 1107M 218M 1124 0 0 0 0 0 0 0 146 2217 789 24 2 74
Should we wait for one interval before displaying the first line, or
display nothing (or a placeholder like '-')?
Below is a quick patch that illustrates the issue, and implements the
"display nothing" option. With the patch the output looks like:
$ vmstat 1
procs memory page disk faults cpu
r b w avm fre flt re pi po fr sr ad0 in sy cs us sy id
3 0 0 1971M 85M 326 0 0 0 334 5 0 457 3674 1495
2 0 0 1971M 85M 23 0 0 0 0 0 0 301 3634 1209 5 7 88
1 0 0 1971M 85M 74 0 0 0 0 0 0 510 4655 1619 7 3 90
And the patch:
Index: usr.bin/vmstat/vmstat.c
===================================================================
--- usr.bin/vmstat/vmstat.c (revision 214019)
+++ usr.bin/vmstat/vmstat.c (working copy)
@@ -658,6 +658,7 @@
int ncpus, maxid;
u_long cpumask;
int rate_adj;
+ int have_prev_cp_times = 0;
uptime = getuptime();
halfuptime = uptime / 2;
@@ -803,10 +804,13 @@
(unsigned long)rate(sum.v_intr - osum.v_intr),
(unsigned long)rate(sum.v_syscall - osum.v_syscall),
(unsigned long)rate(sum.v_swtch - osum.v_swtch));
- if ...
