scx_loader: Add initial automatic scheduler switching via --monitor-no-dbus

Exposes an option --monitor-no-dbus in scx_loader that will monitor CPU
utilization and start scx_lavd when any CPU exceeds 90% for more than 5
seconds. scx_lavd will be terminated if all CPUs are below 90% for
more than 30 seconds. When this flag is specified, scx_loader's
dbus functionality is not utilized.

Cargo.lock

@@ -953,7 +953,7 @@ dependencies = [
  "iana-time-zone-haiku",
  "js-sys",
  "wasm-bindgen",
- "windows-core",
+ "windows-core 0.52.0",
 ]
 
 [[package]]
@@ -1247,6 +1247,15 @@ dependencies = [
  "minimal-lexical",
 ]
 
+[[package]]
+name = "ntapi"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e8a3895c6391c39d7fe7ebc444a87eb2991b2a0bc718fdabd071eec617fc68e4"
+dependencies = [
+ "winapi",
+]
+
 [[package]]
 name = "num-conv"
 version = "0.1.0"
@@ -1546,6 +1555,26 @@ dependencies = [
  "bitflags 2.6.0",
 ]
 
+[[package]]
+name = "rayon"
+version = "1.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b418a60154510ca1a002a752ca9714984e21e4241e804d32555251faf8b78ffa"
+dependencies = [
+ "either",
+ "rayon-core",
+]
+
+[[package]]
+name = "rayon-core"
+version = "1.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1465873a3dfdaa8ae7cb14b4383657caab0b3e8a0aa9ae8e04b044854c8dfce2"
+dependencies = [
+ "crossbeam-deque",
+ "crossbeam-utils",
+]
+
 [[package]]
 name = "redox_syscall"
 version = "0.5.3"
@@ -1714,6 +1743,7 @@ dependencies = [
  "log",
  "nix 0.29.0",
  "serde",
+ "sysinfo",
  "tokio",
  "zbus",
  "zvariant",
@@ -2038,6 +2068,20 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "sysinfo"
+version = "0.31.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "355dbe4f8799b304b05e1b0f05fc59b2a18d36645cf169607da45bde2f69a1be"
+dependencies = [
+ "core-foundation-sys",
+ "libc",
+ "memchr",
+ "ntapi",
+ "rayon",
+ "windows",
+]
+
 [[package]]
 name = "tap"
 version = "1.0.1"
@@ -2442,6 +2486,16 @@ version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
 
+[[package]]
+name = "windows"
+version = "0.57.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "12342cb4d8e3b046f3d80effd474a7a02447231330ef77d71daa6fbc40681143"
+dependencies = [
+ "windows-core 0.57.0",
+ "windows-targets 0.52.6",
+]
+
 [[package]]
 name = "windows-core"
 version = "0.52.0"
@@ -2451,6 +2505,49 @@ dependencies = [
  "windows-targets 0.52.6",
 ]
 
+[[package]]
+name = "windows-core"
+version = "0.57.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d2ed2439a290666cd67ecce2b0ffaad89c2a56b976b736e6ece670297897832d"
+dependencies = [
+ "windows-implement",
+ "windows-interface",
+ "windows-result",
+ "windows-targets 0.52.6",
+]
+
+[[package]]
+name = "windows-implement"
+version = "0.57.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9107ddc059d5b6fbfbffdfa7a7fe3e22a226def0b2608f72e9d552763d3e1ad7"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "windows-interface"
+version = "0.57.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "29bee4b38ea3cde66011baa44dba677c432a78593e202392d1e9070cf2a7fca7"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "windows-result"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5e383302e8ec8515204254685643de10811af0ed97ea37210dc26fb0032647f8"
+dependencies = [
+ "windows-targets 0.52.6",
+]
+
 [[package]]
 name = "windows-sys"
 version = "0.48.0"

rust/scx_loader/Cargo.toml

@@ -14,6 +14,7 @@ ctrlc = { version = "3.1", features = ["termination"] }
 log = "0.4.17"
 nix = { features = ["process", "signal"], default-features = false, version = "0.29" }
 serde = { version = "1.0", features = ["derive"] }
+sysinfo = "0.31.4"
 tokio = { version = "1.39", features = ["macros", "sync", "rt-multi-thread", "process"] }
 zbus = { version = "4", features = ["tokio"], default-features = false }
 zvariant = "4.2"

rust/scx_loader/src/main.rs

@@ -23,6 +23,9 @@ use zbus::interface;
 use zbus::Connection;
 use zvariant::Type;
 use zvariant::Value;
+use clap::Parser;
+use sysinfo::{System};
+use std::{process::{Child}, time::{Duration, Instant}, thread};
 
 #[derive(Debug, Clone, PartialEq)]
 enum SupportedSched {
@@ -63,6 +66,13 @@ struct ScxLoader {
     channel: UnboundedSender<ScxMessage>,
 }
 
+#[derive(Parser, Debug)]
+#[clap(author, version, about, long_about = None)]
+struct Args {
+    #[clap(long, short, action)]
+    monitor_no_dbus: bool,
+}
+
 #[interface(name = "org.scx.Loader")]
 impl ScxLoader {
     /// Get currently running scheduler, in case non is running return "unknown"
@@ -139,11 +149,73 @@ impl ScxLoader {
     }
 }
 
+// Monitors CPU utilization and enables scx_lavd when utilization of any CPUs is > 90%
+async fn monitor_cpu_util() -> Result<()> {
+    let mut system = System::new_all();
+    let mut running_sched: Option<Child> = None;
+    let mut cpu_above_threshold_since: Option<Instant> = None;
+    let mut cpu_below_threshold_since: Option<Instant> = None;
+    
+    let high_utilization_threshold = 90.0;
+    let low_utilization_threshold_duration = Duration::from_secs(30);
+    let high_utilization_trigger_duration = Duration::from_secs(5);
+    
+    loop {
+        system.refresh_cpu_all();
+        
+        let any_cpu_above_threshold = system.cpus().iter().any(|cpu| cpu.cpu_usage() > high_utilization_threshold);
+        
+        if any_cpu_above_threshold {
+            if cpu_above_threshold_since.is_none() {
+                cpu_above_threshold_since = Some(Instant::now());
+            }
+            
+            if cpu_above_threshold_since.unwrap().elapsed() > high_utilization_trigger_duration {
+                if running_sched.is_none() {
+                    println!("CPU Utilization exceeded 90% for 5 seconds, starting scx_lavd");
+                    running_sched = Some(std::process::Command::new("scx_lavd").spawn().expect("Failed to start scx_lavd"));
+                }
+                
+                cpu_below_threshold_since = None;
+            }
+        } else {
+            cpu_above_threshold_since = None;
+            
+            if cpu_below_threshold_since.is_none() {
+                cpu_below_threshold_since = Some(Instant::now());
+            }
+            
+            if cpu_below_threshold_since.unwrap().elapsed() > low_utilization_threshold_duration {
+                if let Some(mut running_sched_loc) = running_sched.take() {
+                    println!("CPU utilization dropped below 90% for more than 30 seconds, exiting latency-aware scheduler");
+                    running_sched_loc.kill().expect("Failed to kill scx_lavd");
+                    let lavd_exit_status = running_sched_loc.wait().expect("Failed to wait on scx_lavd");
+                    println!("scx_lavd exited with status: {}", lavd_exit_status);
+                }
+            }
+        }
+        
+        thread::sleep(Duration::from_secs(1));
+    }
+}
+
 #[tokio::main]
 async fn main() -> Result<()> {
     // initialize the logger
     logger::init_logger().expect("Failed to initialize logger");
 
+    let args = Args::parse();
+    
+    // If --monitor_no_dbus is passed, start scx_loader as a standard background process
+    // that swaps schedulers out automatically 
+    // based on CPU utilization without registering a dbus interface.
+    if args.monitor_no_dbus {
+        println!("Starting scx_loader monitor as standard process without dbus interface");
+        monitor_cpu_util().await?;
+        return Ok(());
+    }
+    
+    println!("Starting as dbus interface");
     // setup channel
     let (channel, rx) = tokio::sync::mpsc::unbounded_channel::<ScxMessage>();