Rework write 100k bench to have a slow writes & even slower flushes

benches/write.rs

@@ -9,43 +9,51 @@ use tungstenite::{Message, WebSocket};
 
 const MOCK_WRITE_LEN: usize = 8 * 1024 * 1024;
 
-/// `Write` impl that simulates fast writes and slow flushes.
+/// `Write` impl that simulates slowish writes and slow flushes.
 ///
-/// Buffers up to 8 MiB fast on `write`. Each `flush` takes ~100ns.
+/// Each `write` can buffer up to 8 MiB before flushing but takes an additional **~80ns**
-struct MockSlowFlushWrite(Vec<u8>);
+/// to simulate stuff going on in the underlying stream.
+/// Each `flush` takes **~8µs** to simulate flush io.
+struct MockWrite(Vec<u8>);
 
-impl Read for MockSlowFlushWrite {
+impl Read for MockWrite {
     fn read(&mut self, _: &mut [u8]) -> io::Result<usize> {
         Err(io::Error::new(io::ErrorKind::WouldBlock, "reads not supported"))
     }
 }
-impl Write for MockSlowFlushWrite {
+impl Write for MockWrite {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         if self.0.len() + buf.len() > MOCK_WRITE_LEN {
             self.flush()?;
         }
+        // simulate io
+        spin(Duration::from_nanos(80));
         self.0.extend(buf);
         Ok(buf.len())
     }
 
     fn flush(&mut self) -> io::Result<()> {
         if !self.0.is_empty() {
-            // simulate 100ns io
+            // simulate io
-            let a = Instant::now();
+            spin(Duration::from_micros(8));
-            while a.elapsed() < Duration::from_nanos(100) {
-                hint::spin_loop();
-            }
             self.0.clear();
         }
         Ok(())
     }
 }
 
+fn spin(duration: Duration) {
+    let a = Instant::now();
+    while a.elapsed() < duration {
+        hint::spin_loop();
+    }
+}
+
 fn benchmark(c: &mut Criterion) {
     // Writes 100k small json text messages then flushes
     c.bench_function("write 100k small texts then flush", |b| {
         let mut ws = WebSocket::from_raw_socket(
-            MockSlowFlushWrite(Vec::with_capacity(MOCK_WRITE_LEN)),
+            MockWrite(Vec::with_capacity(MOCK_WRITE_LEN)),
             tungstenite::protocol::Role::Server,
             None,
         );