fingerprint: add node attr for reserverable cores (#14694)

* fingerprint: add node attr for reserverable cores

Add an attribute for the number of reservable CPU cores as they may
differ from the existing `cpu.numcores` due to client configuration or
OS support.

Hopefully clarifies some confusion in #14676

* add changelog

* num_reservable_cores -> reservablecores

.changelog/14694.txt

@@ -0,0 +1,3 @@
+```release-note:improvement
+fingerprint: Add node attribute for number of reservable cores: `cpu.num_reservable_cores`
+```

client/fingerprint/cpu.go

@@ -2,6 +2,7 @@ package fingerprint
 
 import (
 	"fmt"
+	"strconv"
 
 	"github.com/hashicorp/nomad/lib/cpuset"
 
@@ -62,7 +63,7 @@ func (f *CPUFingerprint) Fingerprint(req *FingerprintRequest, resp *FingerprintR
 
 	var numCores int
 	if numCores = stats.CPUNumCores(); numCores > 0 {
-		resp.AddAttribute("cpu.numcores", fmt.Sprintf("%d", numCores))
+		resp.AddAttribute("cpu.numcores", strconv.Itoa(numCores))
 		f.logger.Debug("detected core count", "cores", numCores)
 	}
 
@@ -80,6 +81,7 @@ func (f *CPUFingerprint) Fingerprint(req *FingerprintRequest, resp *FingerprintR
 			f.logger.Debug("detected reservable cores", "cpuset", reservableCores)
 		}
 	}
+	resp.AddAttribute("cpu.reservablecores", strconv.Itoa(len(reservableCores)))
 
 	tt := int(stats.TotalTicksAvailable())
 	if cfg.CpuCompute > 0 {

client/fingerprint/cpu_test.go

@@ -67,7 +67,9 @@ func TestCPUFingerprint_OverrideCompute(t *testing.T) {
 	node := &structs.Node{
 		Attributes: make(map[string]string),
 	}
-	cfg := &config.Config{}
+	cfg := &config.Config{
+		ReservableCores: []uint16{0, 1, 2},
+	}
 	var originalCPU int
 
 	{
@@ -82,6 +84,10 @@ func TestCPUFingerprint_OverrideCompute(t *testing.T) {
 			t.Fatalf("expected response to be applicable")
 		}
 
+		if attr := response.Attributes["cpu.reservablecores"]; attr != "3" {
+			t.Fatalf("expected cpu.reservablecores == 3 but found %s", attr)
+		}
+
 		if response.Resources.CPU == 0 {
 			t.Fatalf("expected fingerprint of cpu of but found 0")
 		}
@@ -111,5 +117,9 @@ func TestCPUFingerprint_OverrideCompute(t *testing.T) {
 		if response.Attributes["cpu.totalcompute"] != strconv.Itoa(cfg.CpuCompute) {
 			t.Fatalf("expected override cpu.totalcompute of %d but found %s", cfg.CpuCompute, response.Attributes["cpu.totalcompute"])
 		}
+
+		if attr := response.Attributes["cpu.reservablecores"]; attr != "3" {
+			t.Fatalf("expected cpu.reservablecores == 3 but found %s", attr)
+		}
 	}
 }

website/content/docs/runtime/interpolation.mdx

@@ -169,7 +169,13 @@ Below is a table documenting common node properties:
       <td>
         <code>{'${attr.cpu.numcores}'}</code>
       </td>
-      <td>Number of CPU cores on the client</td>
+      <td>Number of CPU cores on the client. May differ from how many cores are available for reservation due to OS or configuration. See <code>cpu.reservablecores</code>.</td>
+    </tr>
+    <tr>
+      <td>
+        <code>{'${attr.cpu.reservablecores}'}</code>
+      </td>
+      <td>Number of CPU cores on the client avaible for scheduling. Number of cores used by the scheduler when placing work with <code>resources.cores</code> set.</td>
     </tr>
     <tr>
       <td>