From b101884e2ef31aca46b5f36325b7d3c11009e976 Mon Sep 17 00:00:00 2001
From: Markus Lehtonen <markus.lehtonen@linux.intel.com>
Date: Tue, 16 Feb 2021 13:14:57 +0200
Subject: [PATCH] rdt: implement GetCPUs() and SetCPUs()

Functionality for associating CPUs with classes. Under the hood
goresctrl will write the given CPU ids to the "cpus_list" file of the
corresponding resctrl group.

The hierarchy between task and cpu lists is as follows (imposed by the
resctrl filesystem):
1. If a process PID is in the tasks file of a non-root class then that
   class is in effect
2. Else, if a process is running on a CPU that is associated with a class,
   then this class is in effect
3. Else the root class is in effect
---
 pkg/rdt/rdt.go      | 27 +++++++++++++++++++++++++++
 pkg/rdt/rdt_test.go | 31 +++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+)

diff --git a/pkg/rdt/rdt.go b/pkg/rdt/rdt.go
index d67f8d8..d881fe0 100644
--- a/pkg/rdt/rdt.go
+++ b/pkg/rdt/rdt.go
@@ -87,6 +87,12 @@ type ResctrlGroup interface {
 	// AddPids assigns the given process ids to the group
 	AddPids(pids ...string) error
 
+	// GetCPUs returns the cpu ids associated with the group
+	GetCPUs() (string, error)
+
+	// SetCPUs associates the given cpu ids with the group
+	SetCPUs(cpus ...string) error
+
 	// GetMonData retrieves the monitoring data of the group
 	GetMonData() MonData
 }
@@ -644,6 +650,27 @@ func (r *resctrlGroup) AddPids(pids ...string) error {
 	return nil
 }
 
+func (r *resctrlGroup) GetCPUs() (string, error) {
+	data, err := rdt.readRdtFile(r.relPath("cpus_list"))
+	if err != nil {
+		return "", err
+	}
+	return strings.TrimSpace(string(data)), nil
+}
+
+func (r *resctrlGroup) SetCPUs(cpus ...string) error {
+	f, err := os.OpenFile(r.path("cpus_list"), os.O_WRONLY, 0644)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	if _, err := f.WriteString(strings.Join(cpus, ",")); err != nil {
+		return rdtError("failed to associate cpus %v to class %q: %v", cpus, r.name, rdt.cmdError(err))
+	}
+	return nil
+}
+
 func (r *resctrlGroup) GetMonData() MonData {
 	m := MonData{}
 
diff --git a/pkg/rdt/rdt_test.go b/pkg/rdt/rdt_test.go
index d10df39..71af784 100644
--- a/pkg/rdt/rdt_test.go
+++ b/pkg/rdt/rdt_test.go
@@ -222,6 +222,9 @@ partitions:
 	if err := cls.AddPids("99"); err != nil {
 		t.Fatalf("AddPids() failed: %v", err)
 	}
+	if err := cls.SetCPUs("1"); err != nil {
+		t.Fatalf("SetCPUs() failed: %v", err)
+	}
 
 	// Configuration should fail as "Stale" class has pids assigned to it
 	if err := SetConfig(conf, false); err == nil {
@@ -286,6 +289,23 @@ partitions:
 
 	mockFs.verifyTextFile(rdt.classes["Guaranteed"].relPath("tasks"), "10\n11\n12\n")
 
+	// Verify assigning CPUs to classes (ctrl groups)
+	if p, err := cls.GetCPUs(); err != nil {
+		t.Errorf("GetCPUs() failed: %v", err)
+	} else if !cmp.Equal(p, "") {
+		t.Errorf("GetCPUs() returned %s, expected an empty string", p)
+	}
+	cpus := []string{"4", "10-13"}
+	if err := cls.SetCPUs(cpus...); err != nil {
+		t.Errorf("SetCPUs() failed: %v", err)
+	}
+	if p, err := cls.GetCPUs(); err != nil {
+		t.Errorf("GetCPUs() failed: %v", err)
+	} else if !cmp.Equal(p, strings.Join(cpus, ",")) {
+		t.Errorf("GetCPUs() returned %s, expected %s", p, cpus)
+	}
+	mockFs.verifyTextFile(rdt.classes["Guaranteed"].relPath("cpus_list"), "4,10-13")
+
 	// Verify MonSupported and GetMonFeatures
 	if !MonSupported() {
 		t.Errorf("MonSupported() returned false, expected true")
@@ -376,6 +396,17 @@ partitions:
 	}
 	mockFs.verifyTextFile(rdt.classes["Guaranteed"].monGroups[mgName].relPath("tasks"), "10\n")
 
+	// Verify assigning cpus to monitor group
+	if err := mg.SetCPUs("0-7"); err != nil {
+		t.Errorf("SetCPUs() failed: %v", err)
+	}
+	if p, err := mg.GetCPUs(); err != nil {
+		t.Errorf("GetCPUs() failed: %v", err)
+	} else if !cmp.Equal(p, "0-7") {
+		t.Errorf("GetCPUs() returned %s, expected 0-7", p)
+	}
+	mockFs.verifyTextFile(rdt.classes["Guaranteed"].monGroups[mgName].relPath("cpus_list"), "0-7")
+
 	// Verify monitoring functionality
 	expected := MonData{
 		L3: MonL3Data{