Log gomaxprocs messages (#10506)

Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>

cmd/prometheus/main.go

@@ -570,8 +570,11 @@ func main() {
 	)
 
 	if cfg.enableAutoGOMAXPROCS {
-		if _, err := maxprocs.Set(); err != nil {
-			level.Warn(logger).Log("msg", "Failed to set GOMAXPROCS automatically", "err", err)
+		l := func(format string, a ...interface{}) {
+			level.Info(logger).Log("component", "automaxprocs", "msg", fmt.Sprintf(strings.TrimPrefix(format, "maxprocs: "), a...))
+		}
+		if _, err := maxprocs.Set(maxprocs.Logger(l)); err != nil {
+			level.Warn(logger).Log("component", "automaxprocs", "msg", "Failed to set GOMAXPROCS automatically", "err", err)
 		}
 	}
 

docs/feature_flags.md

@@ -93,7 +93,4 @@ computed at all.
 
 `--enable-feature=auto-gomaxprocs`
 
-When enabled, GOMAXPROCS variable will be automatically set to match the container CPU limit.
-
-This means that Go runtime will operate as if it had only amount of CPU specified in the container
-CPU limit and not all CPUs on server where it's running.
+When enabled, GOMAXPROCS variable is automatically set to match Linux container CPU quota.