From d53029aba13e92efdcfdd698df3f41a3d25d9ff1 Mon Sep 17 00:00:00 2001
From: dsengupta0628 <dsengupta@precisioninno.com>
Date: Wed, 22 Apr 2026 04:19:34 +0000
Subject: [PATCH] add some debug info for dispatch queue and regression

Signed-off-by: dsengupta0628 <dsengupta@precisioninno.com>
---
 search/Sta.cc                             |  6 +++++
 search/test/CMakeLists.txt                |  1 +
 search/test/search_kahns_bfs_dispatch.ok  |  4 +++
 search/test/search_kahns_bfs_dispatch.tcl | 31 +++++++++++++++++++++++
 4 files changed, 42 insertions(+)
 create mode 100644 search/test/search_kahns_bfs_dispatch.ok
 create mode 100644 search/test/search_kahns_bfs_dispatch.tcl

diff --git a/search/Sta.cc b/search/Sta.cc
index 3eee9dbe..f63d4aae 100644
--- a/search/Sta.cc
+++ b/search/Sta.cc
@@ -338,6 +338,12 @@ Sta::setThreadCount1(int thread_count)
     dispatch_queue_ = new DispatchQueue(thread_count);
 }
 
+uint64_t
+Sta::dispatchCallCount() const
+{
+  return dispatch_queue_ ? dispatch_queue_->dispatchCallCount() : 0;
+}
+
 void
 Sta::updateComponentsState()
 {
diff --git a/search/test/CMakeLists.txt b/search/test/CMakeLists.txt
index d3739b5a..ea483061 100644
--- a/search/test/CMakeLists.txt
+++ b/search/test/CMakeLists.txt
@@ -19,6 +19,7 @@ sta_module_tests("search"
     genclk_latch_deep
     genclk_property_report
     json_unconstrained
+    kahns_bfs_dispatch
     latch
     latch_timing
     levelize_loop_disabled
diff --git a/search/test/search_kahns_bfs_dispatch.ok b/search/test/search_kahns_bfs_dispatch.ok
new file mode 100644
index 00000000..91c01401
--- /dev/null
+++ b/search/test/search_kahns_bfs_dispatch.ok
@@ -0,0 +1,4 @@
+Warning 198: ../../examples/gcd_sky130hd.v line 527, module sky130_fd_sc_hd__tapvpwrvgnd_1 not found. Creating black box for TAP_11.
+off_dispatches=203
+on_dispatches=1060
+on_to_off_ratio=5.22x
diff --git a/search/test/search_kahns_bfs_dispatch.tcl b/search/test/search_kahns_bfs_dispatch.tcl
new file mode 100644
index 00000000..269bc572
--- /dev/null
+++ b/search/test/search_kahns_bfs_dispatch.tcl
@@ -0,0 +1,31 @@
+# Performance regression: DispatchQueue dispatch() counts under Kahn's
+# BFS OFF vs ON. The count is a wall-clock-independent proxy for
+# parallel-dispatch overhead, so a shift in the golden signals a real
+# change in the BFS/dispatch strategy.
+
+read_liberty ../../test/sky130hd/sky130hd_tt.lib
+read_verilog ../../examples/gcd_sky130hd.v
+link_design gcd
+
+sta::set_thread_count 2
+source ../../examples/gcd_sky130hd.sdc
+
+# OFF phase: level-based BFS.
+set sta_use_kahns_bfs 0
+set before [sta::dispatch_call_count]
+report_checks -path_delay min_max -group_count 10 > /dev/null
+set off_dispatches [expr {[sta::dispatch_call_count] - $before}]
+
+# ON phase: Kahn's BFS. Invalidate arrivals so the iterators
+# re-propagate through visitParallel instead of returning cached
+# results.
+sta::arrivals_invalid
+set sta_use_kahns_bfs 1
+set before [sta::dispatch_call_count]
+report_checks -path_delay min_max -group_count 10 > /dev/null
+set on_dispatches [expr {[sta::dispatch_call_count] - $before}]
+
+puts "off_dispatches=$off_dispatches"
+puts "on_dispatches=$on_dispatches"
+puts [format "on_to_off_ratio=%.2fx" \
+          [expr {$on_dispatches / double($off_dispatches)}]]