improve performance for cpu line parser

agent/src/cpu.rs

@@ -1,7 +1,8 @@
 use std::collections::HashMap;
+use anyhow::anyhow;
 use common::metrics::CPUBreakdown;
 
-#[derive(Debug, Clone, Copy)]
+#[derive(Default, Debug, Clone, Copy)]
 struct CPUValues {
     pub user: u64,
     pub nice: u64,
@@ -43,26 +44,33 @@ impl CPUStatReader {
     }
 
     fn parse_cpu_line(&mut self, line: &str) -> anyhow::Result<CPUBreakdown> {
-        let parts: Vec<&str> = line.split_whitespace().collect();
+        let mut parts = line.split_whitespace();
 
-        let cpu_name = parts[0].to_string();
+        let cpu_name = parts.next()
+            .ok_or_else(|| anyhow!("missing cpu name"))?
+            .to_string();
 
-        let parse = |num: usize| -> u64 {
-            parts[num].parse().ok().unwrap()
-        };
+        let mut values = CPUValues::default();
+        let mut fields = [
+            &mut values.user,
+            &mut values.nice,
+            &mut values.system,
+            &mut values.idle,
+            &mut values.iowait,
+            &mut values.irq,
+            &mut values.softirq,
+            &mut values.steal,
+            &mut values.guest,
+            &mut values.guest_nice,
+        ];
 
-        let values = CPUValues {
-            user: parse(1),
-            nice: parse(2),
-            system: parse(3),
-            idle: parse(4),
-            iowait: parse(5),
-            irq: parse(6),
-            softirq: parse(7),
-            steal: parse(8),
-            guest: parse(9),
-            guest_nice: parse(10),
-        };
+        for (field, part) in fields.iter_mut().zip(&mut parts) {
+            **field = part.parse()?;
+        }
+
+        if fields.iter().any(|f| **f == 0 && parts.next().is_some()) {
+            return Err(anyhow!("invalid cpu line"));
+        }
 
         let previous = self.previous_stats.get(&cpu_name).copied();
         let percentages = self.calculate_percentages(&values, previous);