From 7219ac94b3d3f878e5b5a843c4ced619e1904c2c Mon Sep 17 00:00:00 2001
From: Robert O'Callahan <rocallahan@google.com>
Date: Tue, 30 Sep 2025 15:42:10 +0000
Subject: [PATCH 1/4] Add YOSYS_MAX_THREADS

---
 kernel/threading.cc | 19 +++++++++++++++++--
 kernel/threading.h  |  4 ++--
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/kernel/threading.cc b/kernel/threading.cc
index 49fddaa7c..dcc044c89 100644
--- a/kernel/threading.cc
+++ b/kernel/threading.cc
@@ -3,6 +3,20 @@
 
 YOSYS_NAMESPACE_BEGIN
 
+static int init_max_threads()
+{
+	const char *v = getenv("YOSYS_MAX_THREADS");
+	if (v == nullptr)
+		return INT32_MAX;
+	return atoi(v);
+}
+
+static int get_max_threads()
+{
+	static int max_threads = init_max_threads();
+	return max_threads;
+}
+
 void DeferredLogs::flush()
 {
 	for (auto &m : logs)
@@ -12,10 +26,11 @@ void DeferredLogs::flush()
 			YOSYS_NAMESPACE_PREFIX log("%s", m.text.c_str());
 }
 
-int ThreadPool::pool_size(int reserved_cores, int max_threads)
+int ThreadPool::pool_size(int reserved_cores, int max_worker_threads)
 {
 #ifdef YOSYS_ENABLE_THREADS
-	int num_threads = std::min<int>(std::thread::hardware_concurrency() - reserved_cores, max_threads);
+	int available_threads = std::min<int>(std::thread::hardware_concurrency(), get_max_threads());
+	int num_threads = std::min(available_threads - reserved_cores, max_worker_threads);
         return std::max(0, num_threads);
 #else
         return 0;
diff --git a/kernel/threading.h b/kernel/threading.h
index c34abf850..b8cd62f87 100644
--- a/kernel/threading.h
+++ b/kernel/threading.h
@@ -127,9 +127,9 @@ class ThreadPool
 public:
 	// Computes the number of worker threads to use.
 	// `reserved_cores` cores are set aside for other threads (e.g. work on the main thread).
-	// `max_threads` --- don't return more workers than this.
+	// `max_worker_threads` --- don't return more workers than this.
 	// The result may be 0.
-	static int pool_size(int reserved_cores, int max_threads);
+	static int pool_size(int reserved_cores, int max_worker_threads);
 
 	// Create a pool of threads running the given closure (parameterized by thread number).
 	// `pool_size` must be the result of a `pool_size()` call.

From fc951a28d39c2135d46b020b9f6ad4be9ee225f6 Mon Sep 17 00:00:00 2001
From: Robert O'Callahan <rocallahan@google.com>
Date: Tue, 30 Sep 2025 18:54:51 +0000
Subject: [PATCH 2/4] Limit YOSYS_MAX_THREADS to 4 when running makefile-tests
 so we don't overload systems when running 'make -j... test'

---
 tests/gen-tests-makefile.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/gen-tests-makefile.sh b/tests/gen-tests-makefile.sh
index e3308506b..a0fb23ac3 100755
--- a/tests/gen-tests-makefile.sh
+++ b/tests/gen-tests-makefile.sh
@@ -9,7 +9,7 @@ generate_target() {
 	echo "all: $target_name"
 	echo ".PHONY: $target_name"
 	echo "$target_name:"
-	printf "\t@%s\n" "$test_command"
+	printf "\t@YOSYS_MAX_THREADS=4 %s\n" "$test_command"
 	printf "\t@echo 'Passed %s'\n" "$target_name"
 }
 

From a871415abf3b6000c6302b35ef7781f9a58c8d87 Mon Sep 17 00:00:00 2001
From: Robert O'Callahan <rocallahan@google.com>
Date: Thu, 27 Nov 2025 21:57:35 +0000
Subject: [PATCH 3/4] Limit YOSYS_MAX_THREADS to 4 when running seed-tests

---
 tests/arch/run-test.sh         | 1 +
 tests/asicworld/run-test.sh    | 1 +
 tests/blif/run-test.sh         | 1 +
 tests/bram/run-test.sh         | 1 +
 tests/common-env.sh            | 1 +
 tests/cxxrtl/run-test.sh       | 1 +
 tests/fmt/run-test.sh          | 1 +
 tests/fsm/run-test.sh          | 1 +
 tests/functional/run-test.sh   | 1 +
 tests/hana/run-test.sh         | 1 +
 tests/liberty/run-test.sh      | 1 +
 tests/memfile/run-test.sh      | 1 +
 tests/memlib/run-test.sh       | 1 +
 tests/opt_share/run-test.sh    | 1 +
 tests/peepopt/run-test.sh      | 1 +
 tests/proc/run-test.sh         | 1 +
 tests/rpc/run-test.sh          | 1 +
 tests/select/run-test.sh       | 1 +
 tests/share/run-test.sh        | 1 +
 tests/simple/run-test.sh       | 1 +
 tests/simple_abc9/run-test.sh  | 1 +
 tests/svinterfaces/run-test.sh | 1 +
 tests/xprop/run-test.sh        | 1 +
 23 files changed, 23 insertions(+)
 create mode 100644 tests/common-env.sh

diff --git a/tests/arch/run-test.sh b/tests/arch/run-test.sh
index 68f925b34..7602717d2 100755
--- a/tests/arch/run-test.sh
+++ b/tests/arch/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 
 set -e
 
diff --git a/tests/asicworld/run-test.sh b/tests/asicworld/run-test.sh
index 5131ed646..c9b4118a7 100755
--- a/tests/asicworld/run-test.sh
+++ b/tests/asicworld/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 
 OPTIND=1
 seed=""    # default to no seed specified
diff --git a/tests/blif/run-test.sh b/tests/blif/run-test.sh
index e9698386e..2e3f5235c 100755
--- a/tests/blif/run-test.sh
+++ b/tests/blif/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 set -e
 for x in *.ys; do
   echo "Running $x.."
diff --git a/tests/bram/run-test.sh b/tests/bram/run-test.sh
index 37fc91d0e..47f24f5dd 100755
--- a/tests/bram/run-test.sh
+++ b/tests/bram/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 
 # run this test many times:
 # MAKE="make -j8" time bash -c 'for ((i=0; i<100; i++)); do echo "-- $i --"; bash run-test.sh || exit 1; done'
diff --git a/tests/common-env.sh b/tests/common-env.sh
new file mode 100644
index 000000000..f3a411280
--- /dev/null
+++ b/tests/common-env.sh
@@ -0,0 +1 @@
+export YOSYS_MAX_THREADS=4
diff --git a/tests/cxxrtl/run-test.sh b/tests/cxxrtl/run-test.sh
index 4b542e180..aa7a0c26c 100755
--- a/tests/cxxrtl/run-test.sh
+++ b/tests/cxxrtl/run-test.sh
@@ -1,4 +1,5 @@
 #!/bin/bash
+source ../common-env.sh
 
 set -ex
 
diff --git a/tests/fmt/run-test.sh b/tests/fmt/run-test.sh
index 88ee6e238..a3402f953 100644
--- a/tests/fmt/run-test.sh
+++ b/tests/fmt/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 
 set -ex
 
diff --git a/tests/fsm/run-test.sh b/tests/fsm/run-test.sh
index dc60c69c4..139ea8261 100755
--- a/tests/fsm/run-test.sh
+++ b/tests/fsm/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 
 # run this test many times:
 # time bash -c 'for ((i=0; i<100; i++)); do echo "-- $i --"; bash run-test.sh || exit 1; done'
diff --git a/tests/functional/run-test.sh b/tests/functional/run-test.sh
index e0bedf8d4..7c38f3190 100755
--- a/tests/functional/run-test.sh
+++ b/tests/functional/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 
 SCRIPT_DIR=$( cd -- "$( dirname -- "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )
 
diff --git a/tests/hana/run-test.sh b/tests/hana/run-test.sh
index 99be37f5e..8533e5544 100755
--- a/tests/hana/run-test.sh
+++ b/tests/hana/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 
 OPTIND=1
 seed=""    # default to no seed specified
diff --git a/tests/liberty/run-test.sh b/tests/liberty/run-test.sh
index 5afdb727e..d5fb65e16 100755
--- a/tests/liberty/run-test.sh
+++ b/tests/liberty/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 set -eo pipefail
 
 for x in *.lib; do
diff --git a/tests/memfile/run-test.sh b/tests/memfile/run-test.sh
index db0ec54ee..44c1e4821 100755
--- a/tests/memfile/run-test.sh
+++ b/tests/memfile/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 
 set -e
 
diff --git a/tests/memlib/run-test.sh b/tests/memlib/run-test.sh
index 5f230a03e..9e95fb255 100755
--- a/tests/memlib/run-test.sh
+++ b/tests/memlib/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 set -eu
 
 OPTIND=1
diff --git a/tests/opt_share/run-test.sh b/tests/opt_share/run-test.sh
index e80cd4214..e3a6e8b7b 100755
--- a/tests/opt_share/run-test.sh
+++ b/tests/opt_share/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 
 # run this test many times:
 # time bash -c 'for ((i=0; i<100; i++)); do echo "-- $i --"; bash run-test.sh || exit 1; done'
diff --git a/tests/peepopt/run-test.sh b/tests/peepopt/run-test.sh
index e9698386e..2e3f5235c 100644
--- a/tests/peepopt/run-test.sh
+++ b/tests/peepopt/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 set -e
 for x in *.ys; do
   echo "Running $x.."
diff --git a/tests/proc/run-test.sh b/tests/proc/run-test.sh
index e9698386e..2e3f5235c 100755
--- a/tests/proc/run-test.sh
+++ b/tests/proc/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 set -e
 for x in *.ys; do
   echo "Running $x.."
diff --git a/tests/rpc/run-test.sh b/tests/rpc/run-test.sh
index 624043750..0d58b0de2 100755
--- a/tests/rpc/run-test.sh
+++ b/tests/rpc/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 set -e
 for x in *.ys; do
   echo "Running $x.."
diff --git a/tests/select/run-test.sh b/tests/select/run-test.sh
index e9698386e..2e3f5235c 100755
--- a/tests/select/run-test.sh
+++ b/tests/select/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 set -e
 for x in *.ys; do
   echo "Running $x.."
diff --git a/tests/share/run-test.sh b/tests/share/run-test.sh
index a7b5fc4a0..0cef580a7 100755
--- a/tests/share/run-test.sh
+++ b/tests/share/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 
 # run this test many times:
 # time bash -c 'for ((i=0; i<100; i++)); do echo "-- $i --"; bash run-test.sh || exit 1; done'
diff --git a/tests/simple/run-test.sh b/tests/simple/run-test.sh
index b9e79f34a..c3711fe3e 100755
--- a/tests/simple/run-test.sh
+++ b/tests/simple/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 
 OPTIND=1
 seed=""    # default to no seed specified
diff --git a/tests/simple_abc9/run-test.sh b/tests/simple_abc9/run-test.sh
index 5669321ac..0b3e5061f 100755
--- a/tests/simple_abc9/run-test.sh
+++ b/tests/simple_abc9/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 
 OPTIND=1
 seed=""    # default to no seed specified
diff --git a/tests/svinterfaces/run-test.sh b/tests/svinterfaces/run-test.sh
index 71bdcd67a..28ce627d9 100755
--- a/tests/svinterfaces/run-test.sh
+++ b/tests/svinterfaces/run-test.sh
@@ -1,4 +1,5 @@
 #/bin/bash -e
+source ../common-env.sh
 
 ./runone.sh  svinterface1
 ./runone.sh  svinterface_at_top
diff --git a/tests/xprop/run-test.sh b/tests/xprop/run-test.sh
index 84b7c4ac4..303c0bb3b 100755
--- a/tests/xprop/run-test.sh
+++ b/tests/xprop/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 set -e
 
 python3 generate.py $@

From 2ca28d964b1133e08e0240de2b905d41951e0186 Mon Sep 17 00:00:00 2001
From: Robert O'Callahan <rocallahan@google.com>
Date: Thu, 27 Nov 2025 22:04:12 +0000
Subject: [PATCH 4/4] Limit YOSYS_MAX_THREADS to 4 for abcopt-tests

---
 tests/aiger/run-test.sh    | 1 +
 tests/alumacc/run-test.sh  | 1 +
 tests/memories/run-test.sh | 1 +
 3 files changed, 3 insertions(+)

diff --git a/tests/aiger/run-test.sh b/tests/aiger/run-test.sh
index ca7339ff0..f0e27088b 100755
--- a/tests/aiger/run-test.sh
+++ b/tests/aiger/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 
 set -e
 
diff --git a/tests/alumacc/run-test.sh b/tests/alumacc/run-test.sh
index e9698386e..2e3f5235c 100644
--- a/tests/alumacc/run-test.sh
+++ b/tests/alumacc/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 set -e
 for x in *.ys; do
   echo "Running $x.."
diff --git a/tests/memories/run-test.sh b/tests/memories/run-test.sh
index 4f1da7ce7..8f83e11a1 100755
--- a/tests/memories/run-test.sh
+++ b/tests/memories/run-test.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+source ../common-env.sh
 
 set -e