Adding cpu usage in cargo log

src/cargo/core/compiler/timings/mod.rs

@@ -262,31 +262,36 @@ impl<'gctx> Timings<'gctx> {
         build_runner: &BuildRunner<'_, '_>,
         error: &Option<anyhow::Error>,
     ) -> CargoResult<()> {
-        if let Some(logger) = build_runner.bcx.logger
-            && let Some(logs) = logger.get_logs()
-        {
-            let timings_path = build_runner
-                .files()
-                .timings_dir()
-                .expect("artifact-dir was not locked");
-            paths::create_dir_all(&timings_path)?;
-            let run_id = logger.run_id();
-            let filename = timings_path.join(format!("cargo-timing-{run_id}.html"));
-            let mut f = BufWriter::new(paths::create(&filename)?);
+        if let Some(logger) = build_runner.bcx.logger {
+            // Log CPU usage data so it can be reconstructed by `cargo report timings`.
+            for &(elapsed, usage) in &self.cpu_usage {
+                logger.log(LogMessage::CpuUsage { elapsed, usage });
+            }
 
-            let mut ctx = prepare_context(logs.into_iter(), run_id)?;
-            ctx.error = error;
-            ctx.cpu_usage = &self.cpu_usage;
-            report::write_html(ctx, &mut f)?;
+            if let Some(logs) = logger.get_logs() {
+                let timings_path = build_runner
+                    .files()
+                    .timings_dir()
+                    .expect("artifact-dir was not locked");
+                paths::create_dir_all(&timings_path)?;
+                let run_id = logger.run_id();
+                let filename = timings_path.join(format!("cargo-timing-{run_id}.html"));
+                let mut f = BufWriter::new(paths::create(&filename)?);
 
-            let unstamped_filename = timings_path.join("cargo-timing.html");
-            paths::link_or_copy(&filename, &unstamped_filename)?;
+                let mut ctx = prepare_context(logs.into_iter(), run_id)?;
+                ctx.error = error;
+                ctx.cpu_usage = std::borrow::Cow::Borrowed(&self.cpu_usage);
+                report::write_html(ctx, &mut f)?;
 
-            let mut shell = self.gctx.shell();
-            let timing_path = std::env::current_dir().unwrap_or_default().join(&filename);
-            let link = shell.err_file_hyperlink(&timing_path);
-            let msg = format!("report saved to {link}{}{link:#}", timing_path.display(),);
-            shell.status_with_color("Timing", msg, &style::NOTE)?;
+                let unstamped_filename = timings_path.join("cargo-timing.html");
+                paths::link_or_copy(&filename, &unstamped_filename)?;
+
+                let mut shell = self.gctx.shell();
+                let timing_path = std::env::current_dir().unwrap_or_default().join(&filename);
+                let link = shell.err_file_hyperlink(&timing_path);
+                let msg = format!("report saved to {link}{}{link:#}", timing_path.display(),);
+                shell.status_with_color("Timing", msg, &style::NOTE)?;
+            }
         }
         Ok(())
     }

src/cargo/core/compiler/timings/report.rs

@@ -108,7 +108,7 @@ pub struct RenderContext<'a> {
     /// Recorded CPU states, stored as tuples. First element is when the
     /// recording was taken and second element is percentage usage of the
     /// system.
-    pub cpu_usage: &'a [(f64, f64)],
+    pub cpu_usage: Cow<'a, [(f64, f64)]>,
     /// Compiler version info, i.e., `rustc 1.92.0-beta.2 (0a411606e 2025-10-31)`.
     pub rustc_version: String,
     /// The host triple (arch-platform-OS).
@@ -257,7 +257,7 @@ fn write_js_data(ctx: &RenderContext<'_>, f: &mut impl Write) -> CargoResult<()>
     writeln!(
         f,
         "const CPU_USAGE = {};",
-        serde_json::to_string_pretty(&ctx.cpu_usage)?
+        serde_json::to_string_pretty(ctx.cpu_usage.as_ref())?
     )?;
     Ok(())
 }

src/cargo/ops/cargo_report/timings.rs

@@ -156,6 +156,8 @@ where
 
     let mut requested_units: HashSet<UnitIndex> = HashSet::new();
 
+    let mut cpu_usage: Vec<(f64, f64)> = Vec::new();
+
     for msg in log {
         match msg {
             LogMessage::BuildStarted {
@@ -327,6 +329,9 @@ where
                     tracing::warn!("unit {index} ended, but it has no start recorded");
                 }
             },
+            LogMessage::CpuUsage { elapsed, usage } => {
+                cpu_usage.push((elapsed, usage));
+            }
             _ => {} // skip non-timing logs
         }
     }
@@ -382,6 +387,7 @@ where
     ctx.unit_data = unit_data;
     ctx.concurrency = compute_concurrency(&ctx.unit_data);
     ctx.requested_targets = platform_targets.into_iter().sorted_unstable().collect();
+    ctx.cpu_usage = std::borrow::Cow::Owned(cpu_usage);
 
     Ok(ctx)
 }

src/cargo/util/log_message.rs

@@ -152,6 +152,13 @@ pub enum LogMessage {
         #[serde(default, skip_serializing_if = "Option::is_none")]
         cause: Option<DirtyReason>,
     },
+    /// Emitted periodically with CPU usage samples.
+    CpuUsage {
+        /// Seconds elapsed from build start.
+        elapsed: f64,
+        /// CPU usage percentage (0.0 to 100.0).
+        usage: f64,
+    },
 }
 
 /// Cargo target information.

tests/testsuite/build_analysis.rs

@@ -173,7 +173,8 @@ fn log_msg_timing_info() {
     "reason": "unit-finished",
     "run_id": "[..]T[..]Z-[..]",
     "timestamp": "[..]T[..]Z"
-  }
+  },
+  "{...}"
 ]
 "#]]
         .is_json()
@@ -319,7 +320,8 @@ fn log_msg_timing_info_section_timings() {
     "reason": "unit-finished",
     "run_id": "[..]T[..]Z-[..]",
     "timestamp": "[..]T[..]Z"
-  }
+  },
+  "{...}"
 ]
 "#]]
         .is_json()