Default GOMAXPROCS to 1 (#2530)

Avoid running on all CPUs by limiting the Go runtime to one CPU by
default. Avoids having Go routines schedule on every CPU, driving up the
visible run queue length on high CPU count systems.

This also helps workaround a kernel deadlock issue with reading from
sysfs concurrently.

See:
* https://github.com/prometheus/node_exporter/issues/1880
* https://github.com/prometheus/node_exporter/issues/2500

Signed-off-by: Ben Kochie <superq@gmail.com>

CHANGELOG.md

@@ -5,6 +5,13 @@
 * [ENHANCEMENT]
 * [BUGFIX]
 
+NOTE: This changes the Go runtime "GOMAXPROCS" to 1. This is done to limit the
+  concurrency of the exporter to 1 CPU thread at a time in order to avoid a
+  race condition problem in the Linux kernel (#2500) and parallel IO issues
+  on nodes with high numbers of CPUs/CPU threads (#1880).
+
+* [CHANGE] Default GOMAXPROCS to 1
+
 ## 1.4.0 / 2022-09-24
 
 * [CHANGE] Merge metrics descriptions in textfile collector #2475

node_exporter.go

@@ -20,6 +20,7 @@ import (
 	_ "net/http/pprof"
 	"os"
 	"os/user"
+	"runtime"
 	"sort"
 
 	"github.com/prometheus/common/promlog"
@@ -159,6 +160,9 @@ func main() {
 			"collector.disable-defaults",
 			"Set all collectors to disabled by default.",
 		).Default("false").Bool()
+		maxProcs = kingpin.Flag(
+			"runtime.gomaxprocs", "The target number of CPUs Go will run on (GOMAXPROCS)",
+		).Envar("GOMAXPROCS").Default("1").Int()
 		toolkitFlags = kingpinflag.AddFlags(kingpin.CommandLine, ":9100")
 	)
 
@@ -178,6 +182,8 @@ func main() {
 	if user, err := user.Current(); err == nil && user.Uid == "0" {
 		level.Warn(logger).Log("msg", "Node Exporter is running as root user. This exporter is designed to run as unprivileged user, root is not required.")
 	}
+	runtime.GOMAXPROCS(*maxProcs)
+	level.Debug(logger).Log("msg", "Go MAXPROCS", "procs", *maxProcs)
 
 	http.Handle(*metricsPath, newHandler(!*disableExporterMetrics, *maxRequests, logger))
 	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {