From 48c4f394bee44ba4e77e71517823fbbc278d5c4f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Markus=20B=C3=B6ck?= <markus.boeck02@gmail.com>
Date: Wed, 5 Jun 2024 13:05:05 +0100
Subject: [PATCH 1/2] target: Add `VLT_NUM_THREADS` to threads used by
 verilator

Using more threads in the simulation may lead to a speedup in simulation time, especially when the program running in the simulator makes use of multiple cores.
This PR therefore adds the `VLT_NUM_THREADS` option to `make` to allow users to set the thread number used in the simulator. For backwards compatibility, and since the number of threads is environment and code dependent, the default value of 1 was kept.
---
 target/common/common.mk        | 7 +++++++
 target/snitch_cluster/Makefile | 3 +++
 2 files changed, 10 insertions(+)

diff --git a/target/common/common.mk b/target/common/common.mk
index 55b0c17a2..4d5514196 100644
--- a/target/common/common.mk
+++ b/target/common/common.mk
@@ -44,6 +44,7 @@ EVENTVIS_PY      ?= $(UTIL_DIR)/trace/eventvis.py
 # a two-liner with the OS on the first line, hence the tail -n1
 VERILATOR_ROOT ?= $(dir $(shell $(VERILATOR_SEPP) which verilator | tail -n1))..
 VLT_ROOT       ?= ${VERILATOR_ROOT}
+VLT_NUM_THREADS ?= 1
 
 MATCH_END := '/+incdir+/ s/$$/\/*\/*/'
 MATCH_BGN := 's/+incdir+//g'
@@ -86,7 +87,13 @@ VLT_FLAGS    += -Wno-UNSIGNED
 VLT_FLAGS    += -Wno-UNOPTFLAT
 VLT_FLAGS    += -Wno-fatal
 VLT_FLAGS    += --unroll-count 1024
+ifneq ($(VLT_NUM_THREADS), 1)
+	VLT_FLAGS	 += --threads $(VLT_NUM_THREADS)
+endif
 VLT_CFLAGS   += -std=c++14 -pthread
+ifneq ($(VLT_NUM_THREADS), 1)
+	VLT_CFLAGS	 += -DVL_THREADED=1
+endif
 VLT_CFLAGS   +=-I ${VLT_BUILDDIR} -I $(VLT_ROOT)/include -I $(VLT_ROOT)/include/vltstd -I $(VLT_FESVR)/include -I $(TB_DIR) -I ${MKFILE_DIR}/test
 
 ANNOTATE_FLAGS      ?= -q --keep-time --addr2line=$(ADDR2LINE)
diff --git a/target/snitch_cluster/Makefile b/target/snitch_cluster/Makefile
index fc1b4b700..ba6f7a47f 100644
--- a/target/snitch_cluster/Makefile
+++ b/target/snitch_cluster/Makefile
@@ -103,6 +103,9 @@ VLT_COBJ += $(VLT_BUILDDIR)/tb/tb_bin.o
 VLT_COBJ += $(VLT_BUILDDIR)/vlt/verilated.o
 VLT_COBJ += $(VLT_BUILDDIR)/vlt/verilated_dpi.o
 VLT_COBJ += $(VLT_BUILDDIR)/vlt/verilated_vcd_c.o
+ifneq ($(VLT_NUM_THREADS), 1)
+	VLT_COBJ += $(VLT_BUILDDIR)/vlt/verilated_threads.o
+endif
 # Bootdata
 VLT_COBJ += $(VLT_BUILDDIR)/generated/bootdata.o
 

From dab85ad6acf8278c05eb820e4cc2d292c25dfdbf Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Markus=20B=C3=B6ck?= <markus.boeck02@gmail.com>
Date: Wed, 5 Jun 2024 15:52:51 +0100
Subject: [PATCH 2/2] address review comments

---
 target/common/common.mk        | 10 ++++------
 target/snitch_cluster/Makefile |  4 +---
 2 files changed, 5 insertions(+), 9 deletions(-)

diff --git a/target/common/common.mk b/target/common/common.mk
index 4d5514196..5d743a197 100644
--- a/target/common/common.mk
+++ b/target/common/common.mk
@@ -87,13 +87,11 @@ VLT_FLAGS    += -Wno-UNSIGNED
 VLT_FLAGS    += -Wno-UNOPTFLAT
 VLT_FLAGS    += -Wno-fatal
 VLT_FLAGS    += --unroll-count 1024
-ifneq ($(VLT_NUM_THREADS), 1)
-	VLT_FLAGS	 += --threads $(VLT_NUM_THREADS)
-endif
+VLT_FLAGS	 += --threads $(VLT_NUM_THREADS)
 VLT_CFLAGS   += -std=c++14 -pthread
-ifneq ($(VLT_NUM_THREADS), 1)
-	VLT_CFLAGS	 += -DVL_THREADED=1
-endif
+# Custom test benches including the harness must manually define 'VL_THREADED' if multithreaded.
+# See https://github.com/verilator/verilator/issues/3668#issuecomment-1288989145.
+VLT_CFLAGS	 += -DVL_THREADED
 VLT_CFLAGS   +=-I ${VLT_BUILDDIR} -I $(VLT_ROOT)/include -I $(VLT_ROOT)/include/vltstd -I $(VLT_FESVR)/include -I $(TB_DIR) -I ${MKFILE_DIR}/test
 
 ANNOTATE_FLAGS      ?= -q --keep-time --addr2line=$(ADDR2LINE)
diff --git a/target/snitch_cluster/Makefile b/target/snitch_cluster/Makefile
index ba6f7a47f..d18014b45 100644
--- a/target/snitch_cluster/Makefile
+++ b/target/snitch_cluster/Makefile
@@ -103,9 +103,7 @@ VLT_COBJ += $(VLT_BUILDDIR)/tb/tb_bin.o
 VLT_COBJ += $(VLT_BUILDDIR)/vlt/verilated.o
 VLT_COBJ += $(VLT_BUILDDIR)/vlt/verilated_dpi.o
 VLT_COBJ += $(VLT_BUILDDIR)/vlt/verilated_vcd_c.o
-ifneq ($(VLT_NUM_THREADS), 1)
-	VLT_COBJ += $(VLT_BUILDDIR)/vlt/verilated_threads.o
-endif
+VLT_COBJ += $(VLT_BUILDDIR)/vlt/verilated_threads.o
 # Bootdata
 VLT_COBJ += $(VLT_BUILDDIR)/generated/bootdata.o