scx_utils: expose possible and online cpus from Topology

This exposes possible and online CPUs to schedulers.

Related to #721.

rust/scx_utils/src/topology.rs

@@ -184,6 +184,9 @@ pub struct Topology {
     pub all_llcs: BTreeMap<usize, Arc<Llc>>,
     pub all_cores: BTreeMap<usize, Arc<Core>>,
     pub all_cpus: BTreeMap<usize, Arc<Cpu>>,
+
+    pub online_cpus: Cpumask,
+    pub possible_cpus: Cpumask,
 }
 
 impl Topology {
@@ -233,12 +236,17 @@ impl Topology {
             node.all_cpus = node_cpus;
         }
 
+        let online_cpus = cpus_online()?;
+        let possible_cpus = cpus_possible()?;
+
         Ok(Topology {
             nodes,
             span,
             all_llcs: topo_llcs,
             all_cores: topo_cores,
             all_cpus: topo_cpus,
+            online_cpus,
+            possible_cpus,
         })
     }
 
@@ -339,17 +347,24 @@ impl TopoCtx {
 }
 
 fn cpus_online() -> Result<Cpumask> {
-    let path = "/sys/devices/system/cpu/online";
-    let online = std::fs::read_to_string(&path)?;
-    let online_groups: Vec<&str> = online.split(',').collect();
+    parse_cpus("/sys/devices/system/cpu/online")
+}
+
+fn cpus_possible() -> Result<Cpumask> {
+    parse_cpus("/sys/devices/system/cpu/possible")
+}
+
+fn parse_cpus(path: &str) -> Result<Cpumask> {
+    let cpus = std::fs::read_to_string(&path)?;
+    let cpus: Vec<&str> = cpus.split(',').collect();
     let mut mask = Cpumask::new();
-    for group in online_groups.iter() {
+    for group in cpus.iter() {
         let (min, max) = match sscanf!(group.trim(), "{usize}-{usize}") {
             Ok((x, y)) => (x, y),
             Err(_) => match sscanf!(group.trim(), "{usize}") {
                 Ok(x) => (x, x),
                 Err(_) => {
-                    bail!("Failed to parse online cpus {}", group.trim());
+                    bail!("Failed to parse cpus from {}: {}", path, group.trim());
                 }
             },
         };