Improve CPU resource monitor for Linux systems (#4888)

* Replace free call on linux

* Minor fixes

* Rework CPU info for linux

* Fix typos

* Fix issue with memory monitor

* Add comments

* Remove task run delegates

* Fix for macos

* Expand comments for metrics methods

* Remove unnecessary cancellation exits

* Add FF to disable resource monitor on debug runs

* Minor fix

* Fix warning

* Replace DisableResourceMonitorDebugOutput with EnableResourceMonitorDebugOutput

* Fix typo

* Update variable name

* Fix typo

Author: vmapetr

src/Agent.Sdk/Knob/AgentKnobs.cs

@@ -592,6 +592,12 @@ public class AgentKnobs
             new EnvironmentKnobSource("AGENT_DISABLE_DRAIN_QUEUES_AFTER_TASK"),
             new BuiltInDefaultKnobSource("false"));
 
+        public static readonly Knob EnableResourceMonitorDebugOutput = new Knob(
+            nameof(EnableResourceMonitorDebugOutput),
+            "If true, the agent will show the resource monitor output for debug runs",
+            new RuntimeKnobSource("AZP_ENABLE_RESOURCE_MONITOR_DEBUG_OUTPUT"),
+            new EnvironmentKnobSource("AZP_ENABLE_RESOURCE_MONITOR_DEBUG_OUTPUT"),
+            new BuiltInDefaultKnobSource("false"));
 
         public static readonly Knob EnableResourceUtilizationWarnings = new Knob(
             nameof(EnableResourceUtilizationWarnings),

src/Agent.Worker/JobRunner.cs

@@ -119,7 +119,14 @@ public async Task<TaskResult> RunAsync(Pipelines.AgentJobRequestMessage message,
 
                 if (string.Equals(systemDebug, "true", StringComparison.OrdinalIgnoreCase))
                 {
-                    _ = resourceDiagnosticManager.RunDebugResourceMonitorAsync();
+                    if (AgentKnobs.EnableResourceMonitorDebugOutput.GetValue(jobContext).AsBoolean())
+                    {
+                        _ = resourceDiagnosticManager.RunDebugResourceMonitorAsync();
+                    }
+                    else
+                    {
+                        jobContext.Debug(StringUtil.Loc("ResourceUtilizationDebugOutputIsDisabled"));
+                    }
                 }
 
                 agentShutdownRegistration = HostContext.AgentShutdownToken.Register(() =>