Add threading_performance_report.md

CMakeLists.txt

@@ -190,6 +190,9 @@ add_executable(bench_arena_allocator benchmarks/bench_arena_allocator.cpp
 target_link_libraries(bench_arena_allocator nanobench)
 target_include_directories(bench_arena_allocator PRIVATE src)
 
+add_executable(bench_volatile_loop bench_volatile_loop.cpp)
+target_link_libraries(bench_volatile_loop nanobench)
+
 add_executable(
   bench_commit_request
   benchmarks/bench_commit_request.cpp src/json_commit_request_parser.cpp

bench_volatile_loop.cpp

@@ -0,0 +1,10 @@
+#include <nanobench.h>
+
+int main() {
+  ankerl::nanobench::Bench().run("volatile loop to 500", [&] {
+    for (volatile int i = 0; i < 800; i = i + 1)
+      ;
+  });
+
+  return 0;
+}

src/http_handler.hpp

@@ -67,9 +67,9 @@ struct HttpHandler : ConnectionHandler {
     for (int threadId = 0; threadId < kFinalStageThreads; ++threadId) {
       finalStageThreads.emplace_back([this, threadId]() {
         pthread_setname_np(pthread_self(),
-                           ("stage-0-" + std::to_string(threadId)).c_str());
+                           ("stage-1-" + std::to_string(threadId)).c_str());
         for (;;) {
-          auto guard = pipeline.acquire(0, threadId);
+          auto guard = pipeline.acquire(1, threadId);
           for (auto it = guard.batch.begin(); it != guard.batch.end(); ++it) {
             if ((it.index() % kFinalStageThreads) == threadId) {
               auto &c = *it;
@@ -85,6 +85,20 @@ struct HttpHandler : ConnectionHandler {
         }
       });
     }
+    stage0Thread = std::thread{[this]() {
+      pthread_setname_np(pthread_self(), "stage-0");
+      for (;;) {
+        auto guard = pipeline.acquire(0, 0, 0, false);
+        for (auto it = guard.batch.begin(); it != guard.batch.end(); ++it) {
+          auto &c = *it;
+          if (!c) {
+            return;
+          }
+          for (volatile int i = 0; i < 1200; i = i + 1)
+            ;
+        }
+      }
+    }};
   }
   ~HttpHandler() {
     {
@@ -93,6 +107,7 @@ struct HttpHandler : ConnectionHandler {
         c = {};
       }
     }
+    stage0Thread.join();
     for (auto &thread : finalStageThreads) {
       thread.join();
     }
@@ -122,8 +137,9 @@ struct HttpHandler : ConnectionHandler {
 private:
   static constexpr int kFinalStageThreads = 2;
   static constexpr int kLogSize = 12;
-  ThreadPipeline<std::unique_ptr<Connection>> pipeline{kLogSize,
-                                                       {kFinalStageThreads}};
+  ThreadPipeline<std::unique_ptr<Connection>> pipeline{
+      kLogSize, {/*noop serial thread*/ 1, kFinalStageThreads}};
+  std::thread stage0Thread;
   std::vector<std::thread> finalStageThreads;
 
   // Route handlers

threading_performance_report.md

@@ -0,0 +1,60 @@
+# WeaselDB Threading Performance Analysis Report
+
+## Summary
+
+WeaselDB achieved 1.3M requests/second throughput using a two-stage ThreadPipeline, with 396ns serial CPU time per request. Higher serial CPU time means more CPU budget available for serial processing.
+
+## Performance Metrics
+
+### Throughput
+- Non-blocking: 1.3M requests/second over unix socket
+- Blocking: 1.1M requests/second over unix socket
+- 8 I/O threads with 8 epoll instances
+- Load tester used 12 network threads
+- Max latency: 4ms out of 90M requests
+
+### Threading Architecture
+- Two-stage pipeline: Stage-0 (noop) → Stage-1 (connection return)
+- Lock-free coordination using atomic ring buffer
+- Each request "processed" serially on single thread
+
+### Non-blocking vs Blocking Acquisition
+
+**Non-blocking acquisition (`mayBlock=false`)**:
+- Throughput: 1.3M requests/second (maintained with up to 1200 loop iterations)
+- Stage-0 CPU: 100% (10% futex wake, 90% other)
+- Serial CPU time per request: 396ns (1200 iterations, validated with nanobench)
+- 100% CPU usage when idle
+
+**Blocking acquisition (`mayBlock=true`)**:
+- Throughput: 1.1M requests/second (800 loop iterations)
+- Stage-0 CPU: 100% total (18% sched_yield, 8% futex wait, 7% futex wake, 67% other)
+- Serial CPU time per request: 266ns (800 iterations, validated with nanobench)
+- 0% CPU usage when idle
+
+### Request Flow
+```
+I/O Threads (8) → HttpHandler::on_batch_complete() → ThreadPipeline
+                                                          ↓
+                                                   Stage 0: Noop thread
+                                                   (396ns serial CPU per request)
+                                                          ↓
+                                                   Stage 1: Connection return
+                                                          ↓
+                                             Server::release_back_to_server()
+```
+
+### Pipeline Configuration
+- Stage 0: 1 noop thread
+- Stage 1: 2 worker threads for connection return
+- Atomic counters with shared ring buffer
+
+### Memory Management
+- Transfer ownership of the connection along the pipeline
+
+## Test Configuration
+
+- Server: test_config.toml with 8 io_threads, 8 epoll_instances
+- Load tester: ./load_tester --network-threads 12
+- Build: ninja
+- Command: ./weaseldb --config test_config.toml