Expose /proc/pressure (#1261)

This enables the collection of pressure stall information as exposed
by the `/proc/pressure` interface added in the 4.20 release of the
Linux kernel.

Closes #1174

Signed-off-by: Daniele Sluijters <daenney@users.noreply.github.com>

collector/pressure_linux.go

@@ -0,0 +1,105 @@
+// Copyright 2019 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build !nopressure
+
+package collector
+
+import (
+	"fmt"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/common/log"
+	"github.com/prometheus/procfs"
+)
+
+var (
+	psiResources = []string{"cpu", "io", "memory"}
+)
+
+type pressureStatsCollector struct {
+	cpu     *prometheus.Desc
+	io      *prometheus.Desc
+	ioFull  *prometheus.Desc
+	mem     *prometheus.Desc
+	memFull *prometheus.Desc
+
+	fs procfs.FS
+}
+
+func init() {
+	registerCollector("pressure", defaultEnabled, NewPressureStatsCollector)
+}
+
+// NewPressureStatsCollector returns a Collector exposing pressure stall information
+func NewPressureStatsCollector() (Collector, error) {
+	fs, err := procfs.NewFS(*procPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open procfs: %v", err)
+	}
+
+	return &pressureStatsCollector{
+		cpu: prometheus.NewDesc(
+			prometheus.BuildFQName(namespace, "pressure", "cpu_waiting_seconds_total"),
+			"Total time in seconds that processes have waited for CPU time",
+			nil, nil,
+		),
+		io: prometheus.NewDesc(
+			prometheus.BuildFQName(namespace, "pressure", "io_waiting_seconds_total"),
+			"Total time in seconds that processes have waited due to IO congestion",
+			nil, nil,
+		),
+		ioFull: prometheus.NewDesc(
+			prometheus.BuildFQName(namespace, "pressure", "io_stalled_seconds_total"),
+			"Total time in seconds no process could make progress due to IO congestion",
+			nil, nil,
+		),
+		mem: prometheus.NewDesc(
+			prometheus.BuildFQName(namespace, "pressure", "memory_waiting_seconds_total"),
+			"Total time in seconds that processes have waited for memory",
+			nil, nil,
+		),
+		memFull: prometheus.NewDesc(
+			prometheus.BuildFQName(namespace, "pressure", "memory_stalled_seconds_total"),
+			"Total time in seconds no process could make progress due to memory congestion",
+			nil, nil,
+		),
+		fs: fs,
+	}, nil
+}
+
+// Update calls procfs.NewPSIStatsForResource for the different resources and updates the values
+func (c *pressureStatsCollector) Update(ch chan<- prometheus.Metric) error {
+	for _, res := range psiResources {
+		log.Debugf("collecting statistics for resource: %s", res)
+		vals, err := c.fs.NewPSIStatsForResource(res)
+		if err != nil {
+			log.Debug("pressure information is unavailable, you need a Linux kernel >= 4.20 and/or CONFIG_PSI enabled for your kernel")
+			return nil
+		}
+		switch res {
+		case "cpu":
+			ch <- prometheus.MustNewConstMetric(c.cpu, prometheus.CounterValue, float64(vals.Some.Total)/1000.0/1000.0)
+		case "io":
+			ch <- prometheus.MustNewConstMetric(c.io, prometheus.CounterValue, float64(vals.Some.Total)/1000.0/1000.0)
+			ch <- prometheus.MustNewConstMetric(c.ioFull, prometheus.CounterValue, float64(vals.Full.Total)/1000.0/1000.0)
+		case "memory":
+			ch <- prometheus.MustNewConstMetric(c.mem, prometheus.CounterValue, float64(vals.Some.Total)/1000.0/1000.0)
+			ch <- prometheus.MustNewConstMetric(c.memFull, prometheus.CounterValue, float64(vals.Full.Total)/1000.0/1000.0)
+		default:
+			log.Debugf("did not account for resource: %s", res)
+		}
+	}
+
+	return nil
+}