feat(inputs.kernel): Add Pressure Stall Information

plugins/inputs/kernel/README.md

@@ -5,13 +5,14 @@ This plugin is only available on Linux.
 The kernel plugin gathers info about the kernel that doesn't fit into other
 plugins. In general, it is the statistics available in `/proc/stat` that are not
 covered by other plugins as well as the value of
-`/proc/sys/kernel/random/entropy_avail` and optionally, Kernel Samepage Merging.
+`/proc/sys/kernel/random/entropy_avail` and optionally, Kernel Samepage Merging
+and Pressure Stall Information.
 
-The metrics are documented in `man proc` under the `/proc/stat` section.
-The metrics are documented in `man 4 random` under the `/proc/stat` section.
+The metrics are documented in `man 5 proc` under the `/proc/stat` section, as
+well as `man 4 random` under the `/proc interfaces` section
+(for `entropy_avail`).
 
 ```text
-
 /proc/sys/kernel/random/entropy_avail
 Contains the value of available entropy
 
@@ -40,10 +41,28 @@ Number of forks since boot.
 ```
 
 Kernel Samepage Merging is generally documented in [kernel documentation][1] and
-the available metrics exposed via sysfs are documented in [admin guide][2]
+the available metrics exposed via sysfs are documented in [admin guide][2].
+
+Pressure Stall Information is exposed through `/proc/pressure` and is documented
+in [kernel documentation][3]. Kernel version 4.20 or later is required.
+Examples of PSI:
+
+```shell
+# /proc/pressure/cpu
+some avg10=1.53 avg60=1.87 avg300=1.73 total=1088168194
+
+# /proc/pressure/memory
+some avg10=0.00 avg60=0.00 avg300=0.00 total=3463792
+full avg10=0.00 avg60=0.00 avg300=0.00 total=1429641
+
+# /proc/pressure/io
+some avg10=0.00 avg60=0.00 avg300=0.00 total=68568296
+full avg10=0.00 avg60=0.00 avg300=0.00 total=54982338
+```
 
 [1]: https://www.kernel.org/doc/html/latest/mm/ksm.html
 [2]: https://www.kernel.org/doc/html/latest/admin-guide/mm/ksm.html#ksm-daemon-sysfs-interface
+[3]: https://www.kernel.org/doc/html/latest/accounting/psi.html
 
 ## Global configuration options <!-- @/docs/includes/plugin_config.md -->
 
@@ -63,6 +82,7 @@ See the [CONFIGURATION.md][CONFIGURATION.md] for more details.
   ## Additional gather options
   ## Possible options include:
   ## * ksm - kernel same-page merging
+  ## * psi - pressure stall information
   # collect = []
 ```
 
@@ -91,11 +111,41 @@ See the [CONFIGURATION.md][CONFIGURATION.md] for more details.
   - ksm_stable_node_dups (integer, number of duplicated KSM pages, `stable_node_dups`)
   - ksm_use_zero_pages (integer, whether empty pages should be treated specially, `use_zero_pages`)
 
+- pressure (if `psi` is included in `collect`)
+  - tags:
+    - resource: cpu, memory, or io
+    - type: some or full
+  - floating-point fields: avg10, avg60, avg300
+  - integer fields: total
+
 ## Example Output
 
+Default config:
+
 ```text
 kernel boot_time=1690487872i,context_switches=321398652i,entropy_avail=256i,interrupts=141868628i,processes_forked=946492i 1691339564000000000
+```
+
+If `ksm` is included in `collect`:
 
+```text
 kernel boot_time=1690487872i,context_switches=321252729i,entropy_avail=256i,interrupts=141783427i,ksm_full_scans=0i,ksm_max_page_sharing=256i,ksm_merge_across_nodes=1i,ksm_pages_shared=0i,ksm_pages_sharing=0i,ksm_pages_to_scan=100i,ksm_pages_unshared=0i,ksm_pages_volatile=0i,ksm_run=0i,ksm_sleep_millisecs=20i,ksm_stable_node_chains=0i,ksm_stable_node_chains_prune_millisecs=2000i,ksm_stable_node_dups=0i,ksm_use_zero_pages=0i,processes_forked=946467i 1691339522000000000
+```
 
+If `psi` is included in `collect`:
+
+```text
+pressure,resource=cpu,type=some avg10=1.53,avg60=1.87,avg300=1.73 1700000000000000000
+pressure,resource=memory,type=some avg10=0.00,avg60=0.00,avg300=0.00 1700000000000000000
+pressure,resource=memory,type=full avg10=0.00,avg60=0.00,avg300=0.00 1700000000000000000
+pressure,resource=io,type=some avg10=0.0,avg60=0.0,avg300=0.0 1700000000000000000
+pressure,resource=io,type=full avg10=0.0,avg60=0.0,avg300=0.0 1700000000000000000
+pressure,resource=cpu,type=some total=1088168194i 1700000000000000000
+pressure,resource=memory,type=some total=3463792i 1700000000000000000
+pressure,resource=memory,type=full total=1429641i 1700000000000000000
+pressure,resource=io,type=some total=68568296i 1700000000000000000
+pressure,resource=io,type=full total=54982338i 1700000000000000000
 ```
+
+Note that the combination for `resource=cpu,type=full` is omitted because it is
+always zero.

plugins/inputs/kernel/kernel.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/plugins/inputs"
+	"github.com/prometheus/procfs"
 )
 
 //go:embed sample.conf
@@ -34,6 +35,8 @@ type Kernel struct {
 	statFile        string
 	entropyStatFile string
 	ksmStatsDir     string
+	psiDir          string
+	procfs          procfs.FS
 }
 
 func (k *Kernel) Init() error {
@@ -45,7 +48,15 @@ func (k *Kernel) Init() error {
 	if k.optCollect["ksm"] {
 		if _, err := os.Stat(k.ksmStatsDir); os.IsNotExist(err) {
 			// ksm probably not enabled in the kernel, bail out early
-			return fmt.Errorf("directory %q does not exist. Is KSM enabled in this kernel?", k.ksmStatsDir)
+			return fmt.Errorf("directory %q does not exist. KSM is not enabled in this kernel", k.ksmStatsDir)
+		}
+	}
+	if k.optCollect["psi"] {
+		procdir := filepath.Dir(k.psiDir)
+		var err error
+		if k.procfs, err = procfs.NewFS(procdir); err != nil {
+			// psi probably not supported in the kernel, bail out early
+			return fmt.Errorf("failed to initialize procfs on %s: %w", procdir, err)
 		}
 	}
 	return nil
@@ -145,12 +156,18 @@ func (k *Kernel) Gather(acc telegraf.Accumulator) error {
 	}
 	acc.AddCounter("kernel", fields, map[string]string{})
 
+	if k.optCollect["psi"] {
+		if err := k.gatherPressure(acc); err != nil {
+			return err
+		}
+	}
+
 	return nil
 }
 
 func (k *Kernel) getProcValueBytes(path string) ([]byte, error) {
 	if _, err := os.Stat(path); os.IsNotExist(err) {
-		return nil, fmt.Errorf("Path %q does not exist", path)
+		return nil, fmt.Errorf("path %q does not exist", path)
 	} else if err != nil {
 		return nil, err
 	}
@@ -183,6 +200,7 @@ func init() {
 			statFile:        "/proc/stat",
 			entropyStatFile: "/proc/sys/kernel/random/entropy_avail",
 			ksmStatsDir:     "/sys/kernel/mm/ksm",
+			psiDir:          "/proc/pressure",
 		}
 	})
 }

plugins/inputs/kernel/kernel_test.go

@@ -200,7 +200,7 @@ func TestKSMEnabledWrongDir(t *testing.T) {
 		ConfigCollect: []string{"ksm"},
 	}
 
-	require.ErrorContains(t, k.Init(), "Is KSM enabled in this kernel?")
+	require.ErrorContains(t, k.Init(), "KSM is not enabled in this kernel")
 }
 
 func TestKSMDisabledNoKSMTags(t *testing.T) {

plugins/inputs/kernel/psi.go

@@ -0,0 +1,50 @@
+//go:build linux
+
+package kernel
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/influxdata/telegraf"
+	"github.com/prometheus/procfs"
+)
+
+// Gather PSI metrics
+func (k *Kernel) gatherPressure(acc telegraf.Accumulator) error {
+	for _, resource := range []string{"cpu", "memory", "io"} {
+		now := time.Now()
+		psiStats, err := k.procfs.PSIStatsForResource(resource)
+		if err != nil {
+			return fmt.Errorf("failed to read %s pressure: %w", resource, err)
+		}
+
+		stats := map[string]*procfs.PSILine{
+			"some": psiStats.Some,
+			"full": psiStats.Full,
+		}
+
+		for _, typ := range []string{"some", "full"} {
+			if resource == "cpu" && typ == "full" {
+				// resource=cpu,type=full is omitted because it is always zero
+				continue
+			}
+
+			tags := map[string]string{
+				"resource": resource,
+				"type":     typ,
+			}
+			stat := stats[typ]
+
+			acc.AddCounter("pressure", map[string]interface{}{
+				"total": stat.Total,
+			}, tags, now)
+			acc.AddGauge("pressure", map[string]interface{}{
+				"avg10":  stat.Avg10,
+				"avg60":  stat.Avg60,
+				"avg300": stat.Avg300,
+			}, tags, now)
+		}
+	}
+	return nil
+}

plugins/inputs/kernel/psi_test.go

@@ -0,0 +1,76 @@
+//go:build linux
+
+package kernel
+
+import (
+	"testing"
+
+	"github.com/influxdata/telegraf/testutil"
+	"github.com/stretchr/testify/require"
+)
+
+func TestPSIEnabledWrongDir(t *testing.T) {
+	k := Kernel{
+		psiDir:        "testdata/this_directory_does_not_exist/stub",
+		ConfigCollect: []string{"psi"},
+	}
+
+	require.ErrorContains(t, k.Init(), "failed to initialize procfs on ")
+}
+
+func TestPSIStats(t *testing.T) {
+	var acc testutil.Accumulator
+
+	k := Kernel{
+		psiDir:        "testdata/pressure",
+		ConfigCollect: []string{"psi"},
+	}
+	require.NoError(t, k.Init())
+	require.NoError(t, k.gatherPressure(&acc))
+
+	// separate fields for gauges and counters
+	pressureFields := map[string]map[string]interface{}{
+		"some": {
+			"avg10":  float64(10),
+			"avg60":  float64(60),
+			"avg300": float64(300),
+		},
+		"full": {
+			"avg10":  float64(1),
+			"avg60":  float64(6),
+			"avg300": float64(30),
+		},
+	}
+	pressureTotalFields := map[string]map[string]interface{}{
+		"some": {
+			"total": uint64(114514),
+		},
+		"full": {
+			"total": uint64(11451),
+		},
+	}
+
+	for _, typ := range []string{"some", "full"} {
+		for _, resource := range []string{"cpu", "memory", "io"} {
+			if resource == "cpu" && typ == "full" {
+				continue
+			}
+
+			tags := map[string]string{
+				"resource": resource,
+				"type":     typ,
+			}
+
+			acc.AssertContainsTaggedFields(t, "pressure", pressureFields[typ], tags)
+			acc.AssertContainsTaggedFields(t, "pressure", pressureTotalFields[typ], tags)
+		}
+	}
+
+	// The combination "resource=cpu,type=full" should NOT appear anywhere
+	forbiddenTags := map[string]string{
+		"resource": "cpu",
+		"type":     "full",
+	}
+	acc.AssertDoesNotContainsTaggedFields(t, "pressure", pressureFields["full"], forbiddenTags)
+	acc.AssertDoesNotContainsTaggedFields(t, "pressure", pressureTotalFields["full"], forbiddenTags)
+}

plugins/inputs/kernel/sample.conf

@@ -4,4 +4,5 @@
   ## Additional gather options
   ## Possible options include:
   ## * ksm - kernel same-page merging
+  ## * psi - pressure stall information
   # collect = []

plugins/inputs/kernel/testdata/pressure/cpu

@@ -0,0 +1,2 @@
+some avg10=10.00 avg60=60.00 avg300=300.00 total=114514
+full avg10=0.00 avg60=0.00 avg300=0.00 total=0

plugins/inputs/kernel/testdata/pressure/io

@@ -0,0 +1,2 @@
+some avg10=10.00 avg60=60.00 avg300=300.00 total=114514
+full avg10=1.00 avg60=6.00 avg300=30.00 total=11451

plugins/inputs/kernel/testdata/pressure/memory

@@ -0,0 +1,2 @@
+some avg10=10.00 avg60=60.00 avg300=300.00 total=114514
+full avg10=1.00 avg60=6.00 avg300=30.00 total=11451