[hostmetricsreceiver]: support reporting amount of available logical …

…and physical CPUs (#23231)

**Link to tracking Issue:** #22099 

Signed-off-by: Benedikt Bongartz <bongartz@klimlive.de>
Co-authored-by: Pablo Baeyens <pbaeyens31+github@gmail.com>

.chloggen/hostmetricsreceiver_support_cpu_count.yaml

@@ -0,0 +1,21 @@
+# Use this changelog template to create an entry for release notes.
+# If your change doesn't affect end users, such as a test fix or a tooling change,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: hostmetricsreceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Report  logical and physical number of CPUs as metric.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [22099]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: | 
+  Use the `system.cpu.logical.count::enabled` and `system.cpu.physical.count::enabled` flags to enable them

receiver/hostmetricsreceiver/internal/scraper/cpuscraper/cpu_scraper.go

@@ -67,5 +67,17 @@ func (s *scraper) scrape(ctx context.Context) (pmetric.Metrics, error) {
 		return pmetric.NewMetrics(), scrapererror.NewPartialScrapeError(err, metricsLen)
 	}
 
+	numCPU, err := cpu.Counts(false)
+	if err != nil {
+		return pmetric.NewMetrics(), scrapererror.NewPartialScrapeError(err, metricsLen)
+	}
+	s.mb.RecordSystemCPUPhysicalCountDataPoint(now, int64(numCPU))
+
+	numCPU, err = cpu.Counts(true)
+	if err != nil {
+		return pmetric.NewMetrics(), scrapererror.NewPartialScrapeError(err, metricsLen)
+	}
+	s.mb.RecordSystemCPULogicalCountDataPoint(now, int64(numCPU))
+
 	return s.mb.Emit(), nil
 }

receiver/hostmetricsreceiver/internal/scraper/cpuscraper/cpu_scraper_test.go

@@ -335,7 +335,7 @@ func assertDatapointValueAndStringAttributes(t *testing.T, dp pmetric.NumberData
 func assertCPUMetricValid(t *testing.T, metric pmetric.Metric, startTime pcommon.Timestamp) {
 	expected := pmetric.NewMetric()
 	expected.SetName("system.cpu.time")
-	expected.SetDescription("Total CPU seconds broken down by different states.")
+	expected.SetDescription("Total seconds each logical CPU spent on each mode.")
 	expected.SetUnit("s")
 	expected.SetEmptySum()
 	internal.AssertDescriptorEqual(t, expected, metric)
@@ -368,7 +368,7 @@ func assertCPUMetricHasLinuxSpecificStateLabels(t *testing.T, metric pmetric.Met
 func assertCPUUtilizationMetricValid(t *testing.T, metric pmetric.Metric, startTime pcommon.Timestamp) {
 	expected := pmetric.NewMetric()
 	expected.SetName("system.cpu.utilization")
-	expected.SetDescription("Percentage of CPU time broken down by different states.")
+	expected.SetDescription("Difference in system.cpu.time since the last measurement, divided by the elapsed time and number of logical CPUs.")
 	expected.SetUnit("1")
 	expected.SetEmptyGauge()
 	internal.AssertDescriptorEqual(t, expected, metric)

receiver/hostmetricsreceiver/internal/scraper/cpuscraper/documentation.md

@@ -16,7 +16,7 @@ metrics:
 
 ### system.cpu.time
 
-Total CPU seconds broken down by different states.
+Total seconds each logical CPU spent on each mode.
 
 | Unit | Metric Type | Value Type | Aggregation Temporality | Monotonic |
 | ---- | ----------- | ---------- | ----------------------- | --------- |
@@ -26,7 +26,7 @@ Total CPU seconds broken down by different states.
 
 | Name | Description | Values |
 | ---- | ----------- | ------ |
-| cpu | CPU number starting at 0. | Any Str |
+| cpu | Logical CPU number starting at 0. | Any Str |
 | state | Breakdown of CPU usage by type. | Str: ``idle``, ``interrupt``, ``nice``, ``softirq``, ``steal``, ``system``, ``user``, ``wait`` |
 
 ## Optional Metrics
@@ -39,9 +39,25 @@ metrics:
     enabled: true
 ```
 
+### system.cpu.logical.count
+
+Number of available logical CPUs.
+
+| Unit | Metric Type | Value Type | Aggregation Temporality | Monotonic |
+| ---- | ----------- | ---------- | ----------------------- | --------- |
+| {cpu} | Sum | Int | Cumulative | false |
+
+### system.cpu.physical.count
+
+Number of available physical CPUs.
+
+| Unit | Metric Type | Value Type | Aggregation Temporality | Monotonic |
+| ---- | ----------- | ---------- | ----------------------- | --------- |
+| {cpu} | Sum | Int | Cumulative | false |
+
 ### system.cpu.utilization
 
-Percentage of CPU time broken down by different states.
+Difference in system.cpu.time since the last measurement, divided by the elapsed time and number of logical CPUs.
 
 | Unit | Metric Type | Value Type |
 | ---- | ----------- | ---------- |
@@ -51,5 +67,5 @@ Percentage of CPU time broken down by different states.
 
 | Name | Description | Values |
 | ---- | ----------- | ------ |
-| cpu | CPU number starting at 0. | Any Str |
+| cpu | Logical CPU number starting at 0. | Any Str |
 | state | Breakdown of CPU usage by type. | Str: ``idle``, ``interrupt``, ``nice``, ``softirq``, ``steal``, ``system``, ``user``, ``wait`` |