(fix): performance.now() should be a minimal op to avoid JSON deserialization overhead

cli/ops/timers.rs

@@ -8,7 +8,11 @@
 //! only need to be able to start, cancel and await a single timer (or Delay, as Tokio
 //! calls it) for an entire Isolate. This is what is implemented here.
 
+use super::dispatch_minimal::minimal_op;
+use super::dispatch_minimal::MinimalOp;
+use crate::metrics::metrics_op;
 use crate::permissions::Permissions;
+use deno_core::error::type_error;
 use deno_core::error::AnyError;
 use deno_core::futures;
 use deno_core::futures::channel::oneshot;
@@ -77,7 +81,7 @@ pub fn init(rt: &mut deno_core::JsRuntime) {
   super::reg_json_sync(rt, "op_global_timer_stop", op_global_timer_stop);
   super::reg_json_sync(rt, "op_global_timer_start", op_global_timer_start);
   super::reg_json_async(rt, "op_global_timer", op_global_timer);
-  super::reg_json_sync(rt, "op_now", op_now);
+  rt.register_op("op_now", metrics_op(minimal_op(op_now)));
   super::reg_json_sync(rt, "op_sleep_sync", op_sleep_sync);
 }
 
@@ -138,26 +142,38 @@ async fn op_global_timer(
 // If the High precision flag is not set, the
 // nanoseconds are rounded on 2ms.
 fn op_now(
-  state: &mut OpState,
-  _args: Value,
-  _zero_copy: &mut [ZeroCopyBuf],
-) -> Result<Value, AnyError> {
-  let start_time = state.borrow::<StartTime>();
+  state: Rc<RefCell<OpState>>,
+  // Arguments are discarded
+  _sync: bool,
+  _x: i32,
+  mut zero_copy: BufVec,
+) -> MinimalOp {
+  match zero_copy.len() {
+    0 => return MinimalOp::Sync(Err(type_error("no buffer specified"))),
+    1 => {}
+    _ => {
+      return MinimalOp::Sync(Err(type_error("Invalid number of arguments")))
+    }
+  }
+
+  let op_state = state.borrow();
+  let start_time = op_state.borrow::<StartTime>();
   let seconds = start_time.elapsed().as_secs();
-  let mut subsec_nanos = start_time.elapsed().subsec_nanos();
-  let reduced_time_precision = 2_000_000; // 2ms in nanoseconds
+  let mut subsec_nanos = start_time.elapsed().subsec_nanos() as f64;
+  let reduced_time_precision = 2_000_000.0; // 2ms in nanoseconds
 
   // If the permission is not enabled
   // Round the nano result on 2 milliseconds
   // see: https://developer.mozilla.org/en-US/docs/Web/API/DOMHighResTimeStamp#Reduced_time_precision
-  if state.borrow::<Permissions>().check_hrtime().is_err() {
+  if op_state.borrow::<Permissions>().check_hrtime().is_err() {
     subsec_nanos -= subsec_nanos % reduced_time_precision;
   }
 
-  Ok(json!({
-    "seconds": seconds,
-    "subsecNanos": subsec_nanos,
-  }))
+  let result = (seconds * 1_000) as f64 + (subsec_nanos / 1_000_000.0);
+
+  (&mut zero_copy[0]).copy_from_slice(&result.to_be_bytes());
+
+  MinimalOp::Sync(Ok(0))
 }
 
 #[derive(Deserialize)]

cli/rt/11_timers.js

@@ -3,6 +3,7 @@
 ((window) => {
   const assert = window.__bootstrap.util.assert;
   const core = window.Deno.core;
+  const { sendSync } = window.__bootstrap.dispatchMinimal;
 
   function opStopGlobalTimer() {
     core.jsonOpSync("op_global_timer_stop");
@@ -16,8 +17,10 @@
     await core.jsonOpAsync("op_global_timer");
   }
 
+  const nowBytes = new Uint8Array(8);
   function opNow() {
-    return core.jsonOpSync("op_now");
+    sendSync("op_now", 0, nowBytes);
+    return new DataView(nowBytes.buffer).getFloat64();
   }
 
   function sleepSync(millis = 0) {

cli/rt/40_performance.js

@@ -43,8 +43,7 @@
   }
 
   function now() {
-    const res = opNow();
-    return res.seconds * 1e3 + res.subsecNanos / 1e6;
+    return opNow();
   }
 
   class PerformanceEntry {