crazy core pinning junk

cpupick/topo_linux.go

@@ -0,0 +1,118 @@
+//go:build linux
+
+package cpupick
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+)
+
+// readTopology probes the NUMA node and physical-core layout of cpus from
+// sysfs. Anything sysfs won't say degrades toward flatTopology: an unknown
+// node becomes node 0, an unknown core becomes a core of its own — either
+// way the corresponding arrange rule becomes a no-op instead of a wrong
+// answer.
+func readTopology(cpus []int) topology {
+	return readTopologyFrom("/sys/devices/system/node", "/sys/devices/system/cpu", cpus)
+}
+
+func readTopologyFrom(nodeDir, cpuDir string, cpus []int) topology {
+	coreOf, zeroCore := coreGroups(cpuDir, cpus)
+	return topology{
+		nodeOf:   numaNodes(nodeDir, cpus),
+		coreOf:   coreOf,
+		zeroCore: zeroCore,
+	}
+}
+
+// numaNodes maps each cpu to its NUMA node via
+// /sys/devices/system/node/nodeN/cpulist. CPUs no node claims (or no node
+// dirs at all: VMs, non-NUMA kernels) land on node 0.
+func numaNodes(nodeDir string, cpus []int) map[int]int {
+	out := make(map[int]int, len(cpus))
+	for _, c := range cpus {
+		out[c] = 0
+	}
+	entries, err := os.ReadDir(nodeDir)
+	if err != nil {
+		return out
+	}
+	want := make(map[int]bool, len(cpus))
+	for _, c := range cpus {
+		want[c] = true
+	}
+	for _, e := range entries {
+		id, ok := strings.CutPrefix(e.Name(), "node")
+		if !ok {
+			continue
+		}
+		n, err := strconv.Atoi(id)
+		if err != nil {
+			continue // has_cpu, possible, ... share the prefix
+		}
+		b, err := os.ReadFile(filepath.Join(nodeDir, e.Name(), "cpulist"))
+		if err != nil {
+			continue
+		}
+		list, err := parseCPUList(strings.TrimSpace(string(b)))
+		if err != nil {
+			continue
+		}
+		for _, c := range list {
+			if want[c] {
+				out[c] = n
+			}
+		}
+	}
+	return out
+}
+
+// coreGroups maps each cpu to a dense physical-core id derived from its
+// (physical_package_id, core_id) pair — core_id alone repeats across
+// sockets. CPUs whose topology files are unreadable get a core of their own.
+// The second return is the group id of the core CPU 0 lives on, or -1 when
+// that can't be determined; CPU 0's own files are consulted even when 0 is
+// not a candidate, so its SMT siblings are recognized under cpusets that
+// exclude CPU 0 itself.
+func coreGroups(cpuDir string, cpus []int) (map[int]int, int) {
+	type pkgCore struct{ pkg, core int }
+	pairOf := func(cpu int) (pkgCore, bool) {
+		topoDir := filepath.Join(cpuDir, fmt.Sprintf("cpu%d", cpu), "topology")
+		pkg, err1 := readIntFile(filepath.Join(topoDir, "physical_package_id"))
+		core, err2 := readIntFile(filepath.Join(topoDir, "core_id"))
+		if err1 != nil || err2 != nil {
+			return pkgCore{}, false
+		}
+		return pkgCore{pkg, core}, true
+	}
+
+	ids := map[pkgCore]int{}
+	out := make(map[int]int, len(cpus))
+	next := 0
+	for _, cpu := range cpus {
+		k, ok := pairOf(cpu)
+		if !ok {
+			out[cpu] = next
+			next++
+			continue
+		}
+		id, ok := ids[k]
+		if !ok {
+			id = next
+			next++
+			ids[k] = id
+		}
+		out[cpu] = id
+	}
+
+	zeroCore := -1
+	if k, ok := pairOf(0); ok {
+		if id, ok := ids[k]; ok {
+			zeroCore = id
+		}
+	}
+	return out, zeroCore
+}