From 4823283820dc84813f3ae45bb9640109a0867099 Mon Sep 17 00:00:00 2001
From: Olivier 'reivilibre <olivier@librepush.net>
Date: Sat, 19 Mar 2022 11:18:12 +0000
Subject: [PATCH] Add Tokio benchmark for memory overhead of tasks

---
 .gitignore                     |  4 ++++
 Cargo.toml                     | 11 +++++++++
 src/bin/tokio_task_overhead.rs | 43 ++++++++++++++++++++++++++++++++++
 src/lib.rs                     |  8 +++++++
 4 files changed, 66 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Cargo.toml
 create mode 100644 src/bin/tokio_task_overhead.rs
 create mode 100644 src/lib.rs

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..7a53b1c
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,4 @@
+/target
+Cargo.lock
+
+.idea
\ No newline at end of file
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..0a58d1f
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,11 @@
+[package]
+name = "benches"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+tokio = { version = "1.17.0", features = ["full"] }
+probes = "0.4.1"
+linreg = "0.2.0"
diff --git a/src/bin/tokio_task_overhead.rs b/src/bin/tokio_task_overhead.rs
new file mode 100644
index 0000000..03da5e2
--- /dev/null
+++ b/src/bin/tokio_task_overhead.rs
@@ -0,0 +1,43 @@
+use probes::process_memory::current_rss;
+use std::sync::Arc;
+use tokio::sync::Semaphore;
+
+pub const TASKS_PER_DATA_POINT: usize = 1024;
+/// The first data point is 0 tasks
+pub const DATA_POINTS: usize = 16385;
+
+/// Calculates the memory overhead of Tokio tasks.
+///
+/// Experimental results as of 2022-03-19:
+/// Debug mode: 0.188 kiB/task; initial: 3843.6 kiB
+/// Release mode: 0.188 kiB/task; initial: 2696.2 kiB
+#[tokio::main]
+pub async fn main() {
+    let mut tasks = vec![0f64; DATA_POINTS];
+    let mut rsses = vec![0f64; DATA_POINTS];
+    let mut num_tasks = 0;
+
+    let semaphore = Arc::new(Semaphore::new(0));
+
+    for data_point in 0..DATA_POINTS {
+        if data_point != 0 {
+            for _ in 0..TASKS_PER_DATA_POINT {
+                let semaphore = semaphore.clone();
+                tokio::spawn(async move {
+                    let permit = semaphore.acquire().await.unwrap();
+                    drop(permit);
+                });
+            }
+
+            num_tasks += TASKS_PER_DATA_POINT;
+        }
+
+        rsses[data_point] = current_rss().unwrap() as f64;
+        tasks[data_point] = num_tasks as f64;
+    }
+
+    let (slope, intercept) = linreg::linear_regression::<_, _, f64>(&tasks, &rsses).unwrap();
+    //eprintln!("{:?}", rsses);
+    eprintln!("{:.3} kiB/task; initial: {:.1} kiB", slope, intercept);
+    semaphore.add_permits(16);
+}
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..1b4a90c
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,8 @@
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn it_works() {
+        let result = 2 + 2;
+        assert_eq!(result, 4);
+    }
+}