[src/trunk]: src/usr.bin/systat Instead of getting an estimate of the number ...

[simonb <simonb%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/a5ee0f1da3ee
branches:  trunk
changeset: 984803:a5ee0f1da3ee
user:      simonb <simonb%NetBSD.org@localhost>
date:      Sat Jul 24 13:42:05 2021 +0000

description:
Instead of getting an estimate of the number of kernel buffers,
allocating memory for them, requesting all the metadata contents of
these buffers (and repeating in the unlikely case of the number of
buffers increasing too much since the estimate) and then straight away
throwing all the contents out just to count how many buffers there were,
just get the initial estimate from the kernel and subtract the slop.

Reduces system CPU usage of "systat vm" by approx 80% for any system
with a reasonable number of buffers.

diffstat:

 usr.bin/systat/vmstat.c |  25 +++----------------------
 1 files changed, 3 insertions(+), 22 deletions(-)

diffs (69 lines):

diff -r fe66ebd207f8 -r a5ee0f1da3ee usr.bin/systat/vmstat.c
--- a/usr.bin/systat/vmstat.c   Sat Jul 24 13:28:14 2021 +0000
+++ b/usr.bin/systat/vmstat.c   Sat Jul 24 13:42:05 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vmstat.c,v 1.88 2020/03/02 09:50:12 mrg Exp $  */
+/*     $NetBSD: vmstat.c,v 1.89 2021/07/24 13:42:05 simonb Exp $       */
 
 /*-
  * Copyright (c) 1983, 1989, 1992, 1993
@@ -34,7 +34,7 @@
 #if 0
 static char sccsid[] = "@(#)vmstat.c   8.2 (Berkeley) 1/12/94";
 #endif
-__RCSID("$NetBSD: vmstat.c,v 1.88 2020/03/02 09:50:12 mrg Exp $");
+__RCSID("$NetBSD: vmstat.c,v 1.89 2021/07/24 13:42:05 simonb Exp $");
 #endif /* not lint */
 
 /*
@@ -481,10 +481,8 @@
        static int relabel = 0;
        static int last_disks = 0;
        static u_long bufmem;
-       struct buf_sysctl *buffers;
        int mib[6];
        size_t size;
-       int extraslop = 0;
 
        if (relabel) {
                labelvmstat();
@@ -528,14 +526,12 @@
 
        /* Get number of metadata buffers */
        size = 0;
-       buffers = NULL;
        mib[0] = CTL_KERN;
        mib[1] = KERN_BUF;
        mib[2] = KERN_BUF_ALL;
        mib[3] = KERN_BUF_ALL;
        mib[4] = (int)sizeof(struct buf_sysctl);
        mib[5] = INT_MAX; /* we want them all */
-again:
        if (sysctl(mib, 6, NULL, &size, NULL, 0) < 0) {
                error("can't get buffers size: %s\n", strerror(errno));
                return;
@@ -544,23 +540,8 @@
                error("buffers size is zero: %s\n", strerror(errno));
                return;
        }
-       size += extraslop * sizeof(struct buf_sysctl);
-       buffers = malloc(size);
-       if (buffers == NULL) {
-               error("can't allocate buffers: %s\n", strerror(errno));
-               return;
-       }
-       if (sysctl(mib, 6, buffers, &size, NULL, 0) < 0) {
-               free(buffers);
-               if (extraslop < 1000) {
-                       extraslop += 100;
-                       goto again;
-               }
-               error("can't get buffers: %s\n", strerror(errno));
-               return;
-       }
-       free(buffers);                  /* XXX there must be a better way! */
        nbuf = size / sizeof(struct buf_sysctl);
+       nbuf -= KERN_BUFSLOP;
 
        putint((int) (bufmem / 1024),           MEMROW + 3, MEMCOL + 5, 12);
        putint((int) ((bufmem * 100) + 0.5) / s.uvmexp.pagesize / s.uvmexp.npages,