From 4bde281e5a4b78378c5697afccfd22e7d113f395 Mon Sep 17 00:00:00 2001
From: maurycy <5383+maurycy@users.noreply.github.com>
Date: Sat, 10 Oct 2026 16:50:40 +0200
Subject: [PATCH 1/2] up

---
 .../Library/2026-10-10-13-35-08.gh-issue-149584.Yq2bF7.rst   | 2 ++
 Modules/_remote_debugging/frames.c                           | 5 +++++
 2 files changed, 7 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2026-10-10-13-35-08.gh-issue-149584.Yq2bF7.rst

diff --git a/Misc/NEWS.d/next/Library/2026-10-10-13-35-08.gh-issue-149584.Yq2bF7.rst b/Misc/NEWS.d/next/Library/2026-10-10-13-35-08.gh-issue-149584.Yq2bF7.rst
new file mode 100644
index 000000000000000..7f92a1b19877cd4
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-10-10-13-35-08.gh-issue-149584.Yq2bF7.rst
@@ -0,0 +1,2 @@
+Improve the performance of the Tachyon profiler by avoiding unnecessary remote
+reads of the base frame sentinel. Patch by Maurycy Pawłowski-Wieroński.
diff --git a/Modules/_remote_debugging/frames.c b/Modules/_remote_debugging/frames.c
index f5b9ed72f1f98e9..a8ca3a2c11252d9 100644
--- a/Modules/_remote_debugging/frames.c
+++ b/Modules/_remote_debugging/frames.c
@@ -326,6 +326,11 @@ process_frame_chain(
         }
         assert(frame_count <= MAX_FRAME_CHAIN_DEPTH);
 
+        if (frame_addr == ctx->base_frame_addr
+                && !(unwinder->gc && frame_addr == ctx->gc_frame)) {
+            break;
+        }
+
         if (ctx->chunks && ctx->chunks->count > 0) {
             parse_result = parse_frame_from_chunks(
                 unwinder, &frame, frame_addr, &next_frame_addr, &stackpointer, ctx->chunks);

From 1a5fa063eec8ede56cee8233172bf31c0c20ffcf Mon Sep 17 00:00:00 2001
From: maurycy <5383+maurycy@users.noreply.github.com>
Date: Sun, 11 Oct 2026 09:11:17 +0200
Subject: [PATCH 2/2] komment

---
 Modules/_remote_debugging/frame_cache.c | 5 ++---
 Modules/_remote_debugging/frames.c      | 3 +++
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/Modules/_remote_debugging/frame_cache.c b/Modules/_remote_debugging/frame_cache.c
index 1b2d9a60f408b91..63d1331015a548d 100644
--- a/Modules/_remote_debugging/frame_cache.c
+++ b/Modules/_remote_debugging/frame_cache.c
@@ -318,9 +318,8 @@ frame_cache_store(
     // Validate we have a complete stack before caching.
     // Only cache if last_frame_visited matches base_frame_addr (the sentinel
     // at the bottom of the stack). Note: we use last_frame_visited rather than
-    // addrs[num_addrs-1] because the base frame is visited but not added to the
-    // addrs array (it returns frame==NULL from is_frame_valid due to
-    // owner==FRAME_OWNED_BY_INTERPRETER).
+    // addrs[num_addrs-1] because the base frame's address is not added to the
+    // addrs array.
     if (base_frame_addr != 0 && last_frame_visited != base_frame_addr) {
         // Incomplete stack - don't cache (graceful degradation)
         return 0;
diff --git a/Modules/_remote_debugging/frames.c b/Modules/_remote_debugging/frames.c
index a8ca3a2c11252d9..268939b6f77a20c 100644
--- a/Modules/_remote_debugging/frames.c
+++ b/Modules/_remote_debugging/frames.c
@@ -326,6 +326,9 @@ process_frame_chain(
         }
         assert(frame_count <= MAX_FRAME_CHAIN_DEPTH);
 
+        // The base frame is a sentinel with previous == NULL: reaching it is
+        // enough, no need to read it. Still read it when it is the GC frame
+        // so the <GC> marker gets emitted.
         if (frame_addr == ctx->base_frame_addr
                 && !(unwinder->gc && frame_addr == ctx->gc_frame)) {
             break;