Fix hierarchical `--prof-pgo` (#6213)

include/verilated_profiler.h

@@ -220,12 +220,25 @@ class VlPgoProfiler final {
     // Counters are stored packed, all together to reduce cache effects
     std::array<uint64_t, N_Entries> m_counters{};  // Time spent on this record
     std::vector<Record> m_records;  // Record information
+    const uint64_t
+        m_currentHierBlockCost;  // An original cost of a profiled hier block. During verilation
+                                 // with collected profiling data, costs of hier blocks change
+                                 // thus hashes of original mtasks does not match those from the
+                                 // previous, instrumented, run. We shall not assume that a single
+                                 // top-level mtask will correspond to the hier block as multiple
+                                 // hier block DPIs can be contracted into a single mtask.
+                                 // Therefore, the old cost, from previous instrumented run, is
+                                 // used to stabilize profiled scheduling.
 
 public:
     // METHODS
-    VlPgoProfiler() = default;
+    explicit VlPgoProfiler(uint64_t currentHierBlockCost = 0)
+        : m_currentHierBlockCost{currentHierBlockCost} {}
     ~VlPgoProfiler() = default;
-    void write(const char* modelp, const std::string& filename, bool firstHierCall) VL_MT_SAFE;
+    VL_UNMOVABLE(VlPgoProfiler);
+    VL_UNCOPYABLE(VlPgoProfiler);
+    void writeHeader(const std::string& filename) VL_MT_SAFE;
+    void write(const char* modelp, const std::string& filename) VL_MT_SAFE;
     void addCounter(size_t counter, const std::string& name) {
         VL_DEBUG_IF(assert(counter < N_Entries););
         m_records.emplace_back(Record{name, counter});
@@ -239,8 +252,7 @@ public:
 };
 
 template <std::size_t N_Entries>
-void VlPgoProfiler<N_Entries>::write(const char* modelp, const std::string& filename,
-                                     bool firstHierCall) VL_MT_SAFE {
+void VlPgoProfiler<N_Entries>::writeHeader(const std::string& filename) VL_MT_SAFE {
     static VerilatedMutex s_mutex;
     const VerilatedLockGuard lock{s_mutex};
 
@@ -250,22 +262,38 @@ void VlPgoProfiler<N_Entries>::write(const char* modelp, const std::string& file
     // each will collect is own data correctly.  However when each is
     // destroyed we need to get all the data, not keep overwriting and only
     // get the last model's data.
-    static bool s_firstCall = firstHierCall;
 
-    VL_DEBUG_IF(VL_DBG_MSGF("+prof+vlt+file writing to '%s'\n", filename.c_str()););
-
-    FILE* const fp = std::fopen(filename.c_str(), s_firstCall ? "w" : "a");
+    FILE* const fp = std::fopen(filename.c_str(), "w");
     if (VL_UNLIKELY(!fp)) {
         VL_FATAL_MT(filename.c_str(), 0, "", "+prof+vlt+file file not writable");
     }
-    if (s_firstCall) {
-        // TODO Perhaps merge with verilated_coverage output format, so can
-        // have a common merging and reporting tool, etc.
-        fprintf(fp, "// Verilated model profile-guided optimization data dump file\n");
-        fprintf(fp, "`verilator_config\n");
+
+    VL_DEBUG_IF(VL_DBG_MSGF("+prof+vlt+file initializing '%s'\n", filename.c_str()););
+
+    // TODO Perhaps merge with verilated_coverage output format, so can
+    // have a common merging and reporting tool, etc.
+    fprintf(fp, "// Verilated model profile-guided optimization data dump file\n");
+    fprintf(fp, "`verilator_config\n");
+
+    std::fclose(fp);
+}
+
+template <std::size_t N_Entries>
+void VlPgoProfiler<N_Entries>::write(const char* modelp, const std::string& filename) VL_MT_SAFE {
+    static VerilatedMutex s_mutex;
+    const VerilatedLockGuard lock{s_mutex};
+
+    FILE* const fp = std::fopen(filename.c_str(), "a");
+    if (VL_UNLIKELY(!fp)) {
+        VL_FATAL_MT(filename.c_str(), 0, "", "+prof+vlt+file file not writable");
     }
 
-    s_firstCall = false;
+    VL_DEBUG_IF(VL_DBG_MSGF("+prof+vlt+file writing to '%s'\n", filename.c_str()););
+
+    if (m_currentHierBlockCost) {
+        fprintf(fp, "profile_data -hier-dpi \"%s\" -cost 64'd%lu\n", modelp,
+                m_currentHierBlockCost);
+    }
 
     for (const Record& rec : m_records) {
         fprintf(fp, "profile_data -model \"%s\" -mtask \"%s\" -cost 64'd%" PRIu64 "\n", modelp,

src/V3Control.cpp

@@ -18,6 +18,7 @@
 
 #include "V3Control.h"
 
+#include "V3InstrCount.h"
 #include "V3String.h"
 
 #include <memory>
@@ -574,7 +575,11 @@ public:
                         ProfileDataMode mode = MTASK) {
         if (!m_profileFileLine) m_profileFileLine = fl;
         if (cost == 0) cost = 1;  // Cost 0 means delete (or no data)
-        m_profileData[model][key] += cost;
+        if (mode == MTASK) {
+            m_profileData[model][key] += cost;
+        } else if (mode == HIER_DPI) {
+            m_profileData[model][key] = std::max(m_profileData[model][key], cost);
+        }
         m_mode |= mode;
     }
     bool containsMTaskProfileData() const { return m_mode & MTASK; }
@@ -603,6 +608,16 @@ public:
         return it->second;
     }
     FileLine* getProfileDataFileLine() const { return m_profileFileLine; }  // Maybe null
+    static uint64_t getCurrentHierBlockCost() {
+        if (uint64_t cost = V3Control::getProfileData(v3Global.opt.prefix())) {
+            UINFO(9, "Fetching cost from profile info: " << cost);
+            return cost;
+        } else {
+            cost = V3InstrCount::count(v3Global.rootp()->evalp(), false);
+            UINFO(9, "Evaluating cost: " << cost);
+            return cost;
+        }
+    }
 };
 
 //######################################################################
@@ -797,6 +812,9 @@ void V3Control::contentsPushText(const string& text) { return WildcardContents::
 bool V3Control::containsMTaskProfileData() {
     return V3ControlResolver::s().containsMTaskProfileData();
 }
+uint64_t V3Control::getCurrentHierBlockCost() {
+    return V3ControlResolver::s().getCurrentHierBlockCost();
+}
 
 bool V3Control::waive(const FileLine* filelinep, V3ErrorCode code, const string& message) {
     V3ControlFile* const filep = V3ControlResolver::s().files().resolve(filelinep->filename());

src/V3Control.h

@@ -64,6 +64,7 @@ public:
     static void contentsPushText(const string& text);
 
     static bool containsMTaskProfileData();
+    static uint64_t getCurrentHierBlockCost();
 
     static bool waive(const FileLine* filelinep, V3ErrorCode code, const string& message);
 };

src/V3EmitCSyms.cpp

@@ -491,6 +491,11 @@ void EmitCSyms::emitSymHdr() {
         puts("VlExecutionProfiler* const __Vm_executionProfilerp;\n");
     }
 
+    if (v3Global.opt.profPgo()) {
+        puts("\n// PGO PROFILING\n");
+        puts("VlPgoProfiler<" + std::to_string(ExecMTask::numUsedIds()) + "> _vm_pgoProfiler;\n");
+    }
+
     puts("\n// MODULE INSTANCE STATE\n");
     for (const auto& i : m_scopes) {
         const AstScope* const scopep = i.first;
@@ -509,11 +514,6 @@ void EmitCSyms::emitSymHdr() {
         puts("];\n");
     }
 
-    if (v3Global.opt.profPgo()) {
-        puts("\n// PGO PROFILING\n");
-        puts("VlPgoProfiler<" + std::to_string(ExecMTask::numUsedIds()) + "> _vm_pgoProfiler;\n");
-    }
-
     if (!m_scopeNames.empty()) {  // Scope names
         puts("\n// SCOPE NAMES\n");
         for (const auto& itr : m_scopeNames) {
@@ -728,11 +728,8 @@ void EmitCSyms::emitSymImp() {
         puts("#endif  // VM_TRACE\n");
     }
     if (v3Global.opt.profPgo()) {
-        // Do not overwrite data during the last hierarchical stage.
-        const string firstHierCall
-            = (v3Global.opt.hierBlocks().empty() || v3Global.opt.hierChild()) ? "true" : "false";
         puts("_vm_pgoProfiler.write(\"" + EmitCUtil::topClassName()
-             + "\", _vm_contextp__->profVltFilename(), " + firstHierCall + ");\n");
+             + "\", _vm_contextp__->profVltFilename());\n");
     }
     puts("}\n");
 
@@ -802,6 +799,9 @@ void EmitCSyms::emitSymImp() {
              "__Vm_executionProfilerp{static_cast<VlExecutionProfiler*>(contextp->"
              "enableExecutionProfiler(&VlExecutionProfiler::construct))}\n");
     }
+    if (v3Global.opt.profPgo() && !v3Global.opt.libCreate().empty()) {
+        puts("    , _vm_pgoProfiler{" + std::to_string(v3Global.currentHierBlockCost()) + "}\n");
+    }
 
     puts("    // Setup module instances\n");
     for (const auto& i : m_scopes) {
@@ -835,6 +835,9 @@ void EmitCSyms::emitSymImp() {
 
     if (v3Global.opt.profPgo()) {
         puts("// Configure profiling for PGO\n");
+        if (!v3Global.opt.hierChild()) {
+            puts("_vm_pgoProfiler.writeHeader(_vm_contextp__->profVltFilename());\n");
+        }
         if (v3Global.opt.mtasks()) {
             v3Global.rootp()->topModulep()->foreach([&](const AstExecGraph* execGraphp) {
                 for (const V3GraphVertex& vtx : execGraphp->depGraphp()->vertices()) {

src/V3Global.h

@@ -127,6 +127,7 @@ class V3Global final {
     bool m_hasSCTextSections = false;  // Has `systemc_* sections that need to be emitted
     bool m_useParallelBuild = false;  // Use parallel build for model
     bool m_useRandomizeMethods = false;  // Need to define randomize() class methods
+    uint64_t m_currentHierBlockCost = 0;  // Total cost of this hier block, used for scheduling
 
     // Memory address to short string mapping (for debug)
     std::unordered_map<const void*, std::string>
@@ -214,6 +215,8 @@ public:
     const std::string& ptrToId(const void* p);
     std::thread::id mainThreadId() const { return m_mainThreadId; }
     static std::vector<std::string> verilatedCppFiles();
+    uint64_t currentHierBlockCost() const { return m_currentHierBlockCost; }
+    void currentHierBlockCost(uint64_t cost) { m_currentHierBlockCost = cost; }
 };
 
 extern V3Global v3Global;

src/V3ProtectLib.cpp

@@ -24,8 +24,6 @@
 #include "V3String.h"
 #include "V3Task.h"
 
-#include <list>
-
 VL_DEFINE_DEBUG_FUNCTIONS;
 
 //######################################################################
@@ -104,21 +102,14 @@ class ProtectVisitor final : public VNVisitor {
         txtp->addText(fl, "\n`ifdef VERILATOR\n");
         txtp->addText(fl, "`verilator_config\n");
 
-        // The `eval` function is called inside both update functions. As those functions
-        // are created by text bashing, we need to find cost of `_eval` which is the first function
-        // with a real cost in AST.
-        uint32_t cost = 0;
-        modp->foreach([&cost](AstCFunc* cfuncp) {
-            if (cfuncp->name() == "_eval") cost = V3InstrCount::count(cfuncp, false);
-        });
         txtp->addText(fl, "profile_data -hier-dpi \"" + m_libName
-                              + "_protectlib_combo_update\" -cost 64'd" + std::to_string(cost)
-                              + "\n");
+                              + "_protectlib_combo_update\" -cost 64'd"
+                              + std::to_string(v3Global.currentHierBlockCost()) + "\n");
         txtp->addText(fl, "profile_data -hier-dpi \"" + m_libName
-                              + "_protectlib_seq_update\" -cost 64'd" + std::to_string(cost)
-                              + "\n");
+                              + "_protectlib_seq_update\" -cost 64'd"
+                              + std::to_string(v3Global.currentHierBlockCost()) + "\n");
 
-        // Mark remaining NDA protectlib wrapper DPIs as non-hazardous by deliberately forwarding
+        // Mark remaining NBA protectlib wrapper DPIs as non-hazardous by deliberately forwarding
         // them with non-zero cost.
         // Also, specify hierarchical workers for those tasks for scheduling.
         txtp->addText(fl, "profile_data -hier-dpi \"" + m_libName

src/Verilator.cpp

@@ -34,6 +34,7 @@
 #include "V3Combine.h"
 #include "V3Common.h"
 #include "V3Const.h"
+#include "V3Control.h"
 #include "V3Coverage.h"
 #include "V3CoverageJoin.h"
 #include "V3Dead.h"
@@ -590,6 +591,11 @@ static void process() {
 
             // Create AstCUse to determine what class forward declarations/#includes needed in C
             V3CUse::cUseAll();
+
+            // Evaluate cost of a current hierarchical block
+            if (!v3Global.opt.libCreate().empty()) {
+                v3Global.currentHierBlockCost(V3Control::getCurrentHierBlockCost());
+            }
         }
 
         // Output the text

test_regress/t/t_hier_block_perf.v

@@ -18,6 +18,7 @@ module t (/*AUTOARG*/
 
    generate
       for (genvar i = 0; i < `CORES; ++i) Core core(clk);
+      for (genvar i = 0; i < `CORES; ++i) CoreHier hierCore(clk);
    endgenerate
 endmodule
 
@@ -43,6 +44,15 @@ module Core(input clk);
       Check check(.clk(clk), .crc(crc), .result(result), .rdata(rdata), .rdata2(rdata2));
 endmodule
 
+module CoreHier(input clk);
+   // Dummy logic to have two different hier blocks at the same level.
+   integer cyc = 0;
+   always @(posedge clk) begin
+      cyc += 1;
+      if (cyc == 1) $display("%d", clk);
+   end
+endmodule
+
 module Check(
       input clk,
       output reg [63:0] crc,

test_regress/t/t_pgo_threads_hier.py

@@ -11,11 +11,12 @@ import vltest_bootstrap
 
 test.scenarios('vltmt')
 test.top_filename = "t/t_hier_block_perf.v"
-cycles = 100000
+cycles = 100
 test.sim_time = cycles * 10 + 1000
 
 threads = 2
-flags = ["--hierarchical", "-Wno-UNOPTFLAT", "-DSIM_CYCLES=" + str(cycles)]
+config_file = test.t_dir + "/" + test.name + ".vlt"
+flags = [config_file, "--hierarchical", "-Wno-UNOPTFLAT", "-DSIM_CYCLES=" + str(cycles)]
 
 test.compile(benchmarksim=1, v_flags2=["--prof-pgo"] + flags, threads=threads)
 
@@ -24,15 +25,21 @@ test.execute(all_run_flags=[
     " +verilator+prof+exec+file+/dev/null",
     " +verilator+prof+vlt+file+" + test.obj_dir + "/profile.vlt"])  # yapf:disable
 
+test.file_grep(test.obj_dir + "/profile.vlt", r'profile_data -model "VTest"')
+test.file_grep(test.obj_dir + "/profile.vlt", r'profile_data -model "VCheck"')
+test.file_grep(test.obj_dir + "/profile.vlt", r'profile_data -model "VCoreHier"')
 test.file_grep(test.obj_dir + "/profile.vlt", r'profile_data -model "V' + test.name + '"')
 
+# Check for cost rollovers
+test.file_grep_not(test.obj_dir + "/profile.vlt", r'.*cost 64\'d\d{18}.*')
+
 # Differentiate benchmarksim results
 test.name = test.name + "_optimized"
 test.compile(
     benchmarksim=1,
     # Intentionally no --prof-pgo here to make sure profile data can be read in
     # without it (that is: --prof-pgo has no effect on profile_data hash names)
-    v_flags2=flags,
+    v_flags2=[test.obj_dir + "/profile.vlt"] + flags,
     threads=threads)
 
 test.execute()

test_regress/t/t_pgo_threads_hier.vlt

@@ -8,3 +8,5 @@
 hier_workers -module "Test" -workers 2
 hier_block -module "Check"
 hier_workers -module "Check" -workers 2
+hier_block -module "CoreHier"
+hier_workers -module "CoreHier" -workers 2

test_regress/t/t_pgo_threads_hier_nested.py

@@ -1,45 +0,0 @@
-#!/usr/bin/env python3
-# DESCRIPTION: Verilator: Verilog Test driver/expect definition
-#
-# Copyright 2025 by Wilson Snyder. This program is free software; you
-# can redistribute it and/or modify it under the terms of either the GNU
-# Lesser General Public License Version 3 or the Perl Artistic License
-# Version 2.0.
-# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
-
-import vltest_bootstrap
-
-test.scenarios('vltmt')
-test.top_filename = "t/t_hier_block_perf.v"
-cycles = 100000
-test.sim_time = cycles * 10 + 1000
-
-threads = 2
-config_file = test.t_dir + "/" + test.name + ".vlt"
-flags = [config_file, "--hierarchical", "-Wno-UNOPTFLAT", "-DSIM_CYCLES=" + str(cycles)]
-
-test.compile(benchmarksim=1, v_flags2=["--prof-pgo"] + flags, threads=threads)
-
-test.execute(all_run_flags=[
-    "+verilator+prof+exec+start+0",
-    " +verilator+prof+exec+file+/dev/null",
-    " +verilator+prof+vlt+file+" + test.obj_dir + "/profile.vlt"])  # yapf:disable
-
-test.file_grep(test.obj_dir + "/profile.vlt", r'profile_data -model "VTest"')
-test.file_grep(test.obj_dir + "/profile.vlt", r'profile_data -model "V' + test.name + '"')
-
-# Check for cost rollovers
-test.file_grep_not(test.obj_dir + "/profile.vlt", r'.*cost 64\'d\d{18}.*')
-
-# Differentiate benchmarksim results
-test.name = test.name + "_optimized"
-test.compile(
-    benchmarksim=1,
-    # Intentionally no --prof-pgo here to make sure profile data can be read in
-    # without it (that is: --prof-pgo has no effect on profile_data hash names)
-    v_flags2=flags,
-    threads=threads)
-
-test.execute()
-
-test.passes()