From 9e2b56b7aec560540ef9f49c9444c2c0fc903090 Mon Sep 17 00:00:00 2001
From: Daneel <daneel@sukany.cz>
Date: Sun, 1 Mar 2026 05:23:37 +0100
Subject: [PATCH 11/11] perf: cache UAZoomEnabled() and rate-limit completion
 tracking
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UAZoomEnabled() performs a synchronous Mach IPC roundtrip to the macOS
Accessibility server (~50-200 µs per call).  With three call sites in
the redisplay hot path (ns_draw_window_cursor, ns_update_end fallback,
ns_zoom_track_completion) this adds up to 150-600 µs of IPC overhead
per redisplay cycle.  At 60 fps, that is 9-36 ms/s of pure IPC cost.
The overhead blocks the main thread, extending the inter-frame interval
and making cursor movement feel choppy, especially at the end of large
files where Emacs's own redisplay work is already at its maximum.

* src/nsterm.m (ns_zoom_cached_enabled, ns_zoom_cache_time): New
static variables.
(ns_zoom_enabled_p): New inline wrapper around UAZoomEnabled().
Caches the result for 1 second using CFAbsoluteTimeGetCurrent(), a
near-free VDSO call.  Zoom state changes only on explicit user action
in System Settings, so a 1-second TTL is indistinguishable from
querying on every frame.  Replaces all three UAZoomEnabled() call
sites.
(ns_zoom_track_completion): Add 500 ms rate limit.  Completion
candidate detection requires FOR_EACH_FRAME iteration and
Fget_char_property calls.  Completion state changes at human
interaction speed (well below 2 Hz), so 500 ms polling is
imperceptible while eliminating per-redisplay Lisp overhead.
---
 src/nsterm.m | 43 ++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 40 insertions(+), 3 deletions(-)

diff --git a/src/nsterm.m b/src/nsterm.m
index e3f9466..590287a 100644
--- a/src/nsterm.m
+++ b/src/nsterm.m
@@ -1092,6 +1092,31 @@ static NSRect constrain_frame_rect(NSRect frameRect, bool isFullscreen)
    ivy-current-match, corfu-current that mark the selected candidate.  */
 static bool ns_ax_face_is_selected (Lisp_Object face);
 
+/* Cached wrapper around UAZoomEnabled().
+   UAZoomEnabled() performs a synchronous Mach IPC roundtrip to the
+   macOS Accessibility server (~50-200 µs per call).  With three call
+   sites in the redisplay hot path the overhead accumulates to
+   150-600 µs per frame.  Zoom state only changes on explicit user
+   action in System Settings, so a 1-second TTL is both safe and
+   indistinguishable from querying on every frame.
+
+   Uses CFAbsoluteTimeGetCurrent() (a VDSO read on modern macOS, ~5 ns)
+   to avoid a second IPC roundtrip for time.  */
+static BOOL  ns_zoom_cached_enabled;
+static CFAbsoluteTime ns_zoom_cache_time;
+
+static BOOL
+ns_zoom_enabled_p (void)
+{
+  CFAbsoluteTime now = CFAbsoluteTimeGetCurrent ();
+  if (now - ns_zoom_cache_time > 1.0)
+    {
+      ns_zoom_cached_enabled = UAZoomEnabled ();
+      ns_zoom_cache_time = now;
+    }
+  return ns_zoom_cached_enabled;
+}
+
 /* Scan overlay before-string / after-string properties in the
    selected window for a completion candidate with a "selected"
    face.  Return the 0-based visual line index of the selected
@@ -1215,11 +1240,23 @@ If a completion candidate is selected (overlay or child frame),
 static void
 ns_zoom_track_completion (struct frame *f, EmacsView *view)
 {
-  if (!UAZoomEnabled ())
+  if (!ns_zoom_enabled_p ())
     return;
   if (!WINDOWP (f->selected_window))
     return;
 
+  /* Rate-limit completion scan to 2 Hz.  Completion overlays and
+     child frames change at human interaction speed (<<10 Hz), so
+     checking every 500 ms is indistinguishable from every frame
+     while eliminating per-redisplay FOR_EACH_FRAME iteration.  */
+  {
+    static CFAbsoluteTime last_completion_track;
+    CFAbsoluteTime now = CFAbsoluteTimeGetCurrent ();
+    if (now - last_completion_track < 0.5)
+      return;
+    last_completion_track = now;
+  }
+
   specpdl_ref count = SPECPDL_INDEX ();
   record_unwind_current_buffer ();
 
@@ -1323,7 +1360,7 @@ so the visual offset is (ov_line + 1) * line_h from
      (zoomCursorUpdated is NO).  */
 #if defined (MAC_OS_X_VERSION_MIN_REQUIRED) \
     && MAC_OS_X_VERSION_MIN_REQUIRED >= 101000
-  if (view && !view->zoomCursorUpdated && UAZoomEnabled ()
+  if (view && !view->zoomCursorUpdated && ns_zoom_enabled_p ()
       && !NSIsEmptyRect (view->lastCursorRect))
     {
       NSRect r = view->lastCursorRect;
@@ -3500,7 +3537,7 @@ EmacsView pixels (AppKit, flipped, top-left origin)
 
 #if defined (MAC_OS_X_VERSION_MIN_REQUIRED) \
     && MAC_OS_X_VERSION_MIN_REQUIRED >= 101000
-	if (UAZoomEnabled ())
+	if (ns_zoom_enabled_p ())
 	  {
 	    NSRect windowRect = [view convertRect:r toView:nil];
 	    NSRect screenRect
-- 
2.43.0