Merge pull request grpc#19696 from yunjiaw26/chunkedlist

Improve MPMCQueue Performance

src/core/lib/iomgr/executor/mpmcqueue.cc

@@ -26,18 +26,15 @@ DebugOnlyTraceFlag grpc_thread_pool_trace(false, "thread_pool");
 
 inline void* InfLenFIFOQueue::PopFront() {
   // Caller should already check queue is not empty and has already held the
-  // mutex. This function will only do the job of removal.
+  // mutex. This function will assume that there is at least one element in the
+  // queue (i.e. queue_head_->content is valid).
   void* result = queue_head_->content;
-  Node* head_to_remove = queue_head_;
-  queue_head_ = queue_head_->next;
-
   count_.Store(count_.Load(MemoryOrder::RELAXED) - 1, MemoryOrder::RELAXED);
 
+  // Updates Stats when trace flag turned on.
   if (GRPC_TRACE_FLAG_ENABLED(grpc_thread_pool_trace)) {
     gpr_timespec wait_time =
-        gpr_time_sub(gpr_now(GPR_CLOCK_MONOTONIC), head_to_remove->insert_time);
-
-    // Updates Stats info
+        gpr_time_sub(gpr_now(GPR_CLOCK_MONOTONIC), queue_head_->insert_time);
     stats_.num_completed++;
     stats_.total_queue_time = gpr_time_add(stats_.total_queue_time, wait_time);
     stats_.max_queue_time = gpr_time_max(
@@ -58,44 +55,89 @@ inline void* InfLenFIFOQueue::PopFront() {
             gpr_timespec_to_micros(stats_.busy_queue_time));
   }
 
-  Delete(head_to_remove);
+  queue_head_ = queue_head_->next;
   // Signal waiting thread
-  if (count_.Load(MemoryOrder::RELAXED) > 0 && num_waiters_ > 0) {
-    wait_nonempty_.Signal();
+  if (count_.Load(MemoryOrder::RELAXED) > 0) {
+    TopWaiter()->cv.Signal();
   }
 
   return result;
 }
 
+InfLenFIFOQueue::Node* InfLenFIFOQueue::AllocateNodes(int num) {
+  num_nodes_ = num_nodes_ + num;
+  Node* new_chunk = static_cast<Node*>(gpr_zalloc(sizeof(Node) * num));
+  new_chunk[0].next = &new_chunk[1];
+  new_chunk[num - 1].prev = &new_chunk[num - 2];
+  for (int i = 1; i < num - 1; ++i) {
+    new_chunk[i].prev = &new_chunk[i - 1];
+    new_chunk[i].next = &new_chunk[i + 1];
+  }
+  return new_chunk;
+}
+
+InfLenFIFOQueue::InfLenFIFOQueue() {
+  delete_list_size_ = kDeleteListInitSize;
+  delete_list_ =
+      static_cast<Node**>(gpr_zalloc(sizeof(Node*) * delete_list_size_));
+
+  Node* new_chunk = AllocateNodes(kQueueInitNumNodes);
+  delete_list_[delete_list_count_++] = new_chunk;
+  queue_head_ = queue_tail_ = new_chunk;
+  new_chunk[0].prev = &new_chunk[kQueueInitNumNodes - 1];
+  new_chunk[kQueueInitNumNodes - 1].next = &new_chunk[0];
+
+  waiters_.next = &waiters_;
+  waiters_.prev = &waiters_;
+}
+
 InfLenFIFOQueue::~InfLenFIFOQueue() {
   GPR_ASSERT(count_.Load(MemoryOrder::RELAXED) == 0);
-  GPR_ASSERT(num_waiters_ == 0);
+  for (size_t i = 0; i < delete_list_count_; ++i) {
+    gpr_free(delete_list_[i]);
+  }
+  gpr_free(delete_list_);
 }
 
 void InfLenFIFOQueue::Put(void* elem) {
   MutexLock l(&mu_);
 
-  Node* new_node = New<Node>(elem);
-  if (count_.Load(MemoryOrder::RELAXED) == 0) {
-    if (GRPC_TRACE_FLAG_ENABLED(grpc_thread_pool_trace)) {
-      busy_time = gpr_now(GPR_CLOCK_MONOTONIC);
+  int curr_count = count_.Load(MemoryOrder::RELAXED);
+
+  if (queue_tail_ == queue_head_ && curr_count != 0) {
+    // List is full. Expands list to double size by inserting new chunk of nodes
+    Node* new_chunk = AllocateNodes(curr_count);
+    delete_list_[delete_list_count_++] = new_chunk;
+    // Expands delete list on full.
+    if (delete_list_count_ == delete_list_size_) {
+      delete_list_size_ = delete_list_size_ * 2;
+      delete_list_ = static_cast<Node**>(
+          gpr_realloc(delete_list_, sizeof(Node*) * delete_list_size_));
     }
-    queue_head_ = queue_tail_ = new_node;
-  } else {
-    queue_tail_->next = new_node;
-    queue_tail_ = queue_tail_->next;
+    new_chunk[0].prev = queue_tail_->prev;
+    new_chunk[curr_count - 1].next = queue_head_;
+    queue_tail_->prev->next = new_chunk;
+    queue_head_->prev = &new_chunk[curr_count - 1];
+    queue_tail_ = new_chunk;
   }
-  count_.Store(count_.Load(MemoryOrder::RELAXED) + 1, MemoryOrder::RELAXED);
+  queue_tail_->content = static_cast<void*>(elem);
+
   // Updates Stats info
   if (GRPC_TRACE_FLAG_ENABLED(grpc_thread_pool_trace)) {
     stats_.num_started++;
     gpr_log(GPR_INFO, "[InfLenFIFOQueue Put] num_started:        %" PRIu64,
             stats_.num_started);
+    auto current_time = gpr_now(GPR_CLOCK_MONOTONIC);
+    if (curr_count == 0) {
+      busy_time = current_time;
+    }
+    queue_tail_->insert_time = current_time;
   }
 
-  if (num_waiters_ > 0) {
-    wait_nonempty_.Signal();
-  }
+  count_.Store(curr_count + 1, MemoryOrder::RELAXED);
+  queue_tail_ = queue_tail_->next;
+
+  TopWaiter()->cv.Signal();
 }
 
 void* InfLenFIFOQueue::Get(gpr_timespec* wait_time) {
@@ -108,11 +150,12 @@ void* InfLenFIFOQueue::Get(gpr_timespec* wait_time) {
       start_time = gpr_now(GPR_CLOCK_MONOTONIC);
     }
 
-    num_waiters_++;
+    Waiter self;
+    PushWaiter(&self);
     do {
-      wait_nonempty_.Wait(&mu_);
+      self.cv.Wait(&mu_);
     } while (count_.Load(MemoryOrder::RELAXED) == 0);
-    num_waiters_--;
+    RemoveWaiter(&self);
     if (GRPC_TRACE_FLAG_ENABLED(grpc_thread_pool_trace) &&
         wait_time != nullptr) {
       *wait_time = gpr_time_sub(gpr_now(GPR_CLOCK_MONOTONIC), start_time);
@@ -122,4 +165,19 @@ void* InfLenFIFOQueue::Get(gpr_timespec* wait_time) {
   return PopFront();
 }
 
+void InfLenFIFOQueue::PushWaiter(Waiter* waiter) {
+  waiter->next = waiters_.next;
+  waiter->prev = &waiters_;
+  waiter->next->prev = waiter;
+  waiter->prev->next = waiter;
+}
+
+void InfLenFIFOQueue::RemoveWaiter(Waiter* waiter) {
+  GPR_DEBUG_ASSERT(waiter != &waiters_);
+  waiter->next->prev = waiter->prev;
+  waiter->prev->next = waiter->next;
+}
+
+InfLenFIFOQueue::Waiter* InfLenFIFOQueue::TopWaiter() { return waiters_.next; }
+
 }  // namespace grpc_core

src/core/lib/iomgr/executor/mpmcqueue.h

@@ -54,7 +54,7 @@ class MPMCQueueInterface {
 class InfLenFIFOQueue : public MPMCQueueInterface {
  public:
   // Creates a new MPMC Queue. The queue created will have infinite length.
-  InfLenFIFOQueue() {}
+  InfLenFIFOQueue();
 
   // Releases all resources held by the queue. The queue must be empty, and no
   // one waits on conditional variables.
@@ -66,33 +66,42 @@ class InfLenFIFOQueue : public MPMCQueueInterface {
 
   // Removes the oldest element from the queue and returns it.
   // This routine will cause the thread to block if queue is currently empty.
-  // Argument wait_time should be passed in when turning on the trace flag
-  // grpc_thread_pool_trace (for collecting stats info purpose.)
+  // Argument wait_time should be passed in when trace flag turning on (for
+  // collecting stats info purpose.)
   void* Get(gpr_timespec* wait_time = nullptr);
 
   // Returns number of elements in queue currently.
   // There might be concurrently add/remove on queue, so count might change
   // quickly.
   int count() const { return count_.Load(MemoryOrder::RELAXED); }
 
- private:
-  // For Internal Use Only.
-  // Removes the oldest element from the queue and returns it. This routine
-  // will NOT check whether queue is empty, and it will NOT acquire mutex.
-  // Caller should do the check and acquire mutex before callling.
-  void* PopFront();
-
   struct Node {
-    Node* next;                // Linking
+    Node* next;  // Linking
+    Node* prev;
     void* content;             // Points to actual element
     gpr_timespec insert_time;  // Time for stats
 
-    Node(void* c) : content(c) {
-      next = nullptr;
-      insert_time = gpr_now(GPR_CLOCK_MONOTONIC);
+    Node() {
+      next = prev = nullptr;
+      content = nullptr;
     }
   };
 
+  // For test purpose only. Returns number of nodes allocated in queue.
+  // Any allocated node will be alive until the destruction of the queue.
+  int num_nodes() const { return num_nodes_; }
+
+  // For test purpose only. Returns the initial number of nodes in queue.
+  int init_num_nodes() const { return kQueueInitNumNodes; }
+
+ private:
+  // For Internal Use Only.
+  // Removes the oldest element from the queue and returns it. This routine
+  // will NOT check whether queue is empty, and it will NOT acquire mutex.
+  // Caller MUST check that queue is not empty and must acquire mutex before
+  // callling.
+  void* PopFront();
+
   // Stats of queue. This will only be collect when debug trace mode is on.
   // All printed stats info will have time measurement in microsecond.
   struct Stats {
@@ -115,15 +124,53 @@ class InfLenFIFOQueue : public MPMCQueueInterface {
     }
   };
 
-  Mutex mu_;               // Protecting lock
-  CondVar wait_nonempty_;  // Wait on empty queue on get
-  int num_waiters_ = 0;    // Number of waiters
+  // Node for waiting thread queue. Stands for one waiting thread, should have
+  // exact one thread waiting on its CondVar.
+  // Using a doubly linked list for waiting thread queue to wake up waiting
+  // threads in LIFO order to reduce cache misses.
+  struct Waiter {
+    CondVar cv;
+    Waiter* next;
+    Waiter* prev;
+  };
+
+  // Pushs waiter to the front of queue, require caller held mutex
+  void PushWaiter(Waiter* waiter);
+
+  // Removes waiter from queue, require caller held mutex
+  void RemoveWaiter(Waiter* waiter);
+
+  // Returns pointer to the waiter that should be waken up next, should be the
+  // last added waiter.
+  Waiter* TopWaiter();
+
+  Mutex mu_;        // Protecting lock
+  Waiter waiters_;  // Head of waiting thread queue
+
+  // Initial size for delete list
+  static const int kDeleteListInitSize = 1024;
+  // Initial number of nodes allocated
+  static const int kQueueInitNumNodes = 1024;
+
+  Node** delete_list_ = nullptr;  // Keeps track of all allocated array entries
+                                  // for deleting on destruction
+  size_t delete_list_count_ = 0;  // Number of entries in list
+  size_t delete_list_size_ = 0;   // Size of the list. List will be expanded to
+                                  // double size on full
 
   Node* queue_head_ = nullptr;  // Head of the queue, remove position
   Node* queue_tail_ = nullptr;  // End of queue, insert position
   Atomic<int> count_{0};        // Number of elements in queue
-  Stats stats_;                 // Stats info
-  gpr_timespec busy_time;       // Start time of busy queue
+  int num_nodes_ = 0;           // Number of nodes allocated
+
+  Stats stats_;            // Stats info
+  gpr_timespec busy_time;  // Start time of busy queue
+
+  // Internal Helper.
+  // Allocates an array of nodes of size "num", links all nodes together except
+  // the first node's prev and last node's next. They should be set by caller
+  // manually afterward.
+  Node* AllocateNodes(int num);
 };
 
 }  // namespace grpc_core

test/core/iomgr/mpmcqueue_test.cc

@@ -119,6 +119,57 @@ static void test_FIFO(void) {
   }
 }
 
+// Test if queue's behavior of expanding is correct. (Only does expansion when
+// it gets full, and each time expands to doubled size).
+static void test_space_efficiency(void) {
+  gpr_log(GPR_INFO, "test_space_efficiency");
+  grpc_core::InfLenFIFOQueue queue;
+  for (int i = 0; i < queue.init_num_nodes(); ++i) {
+    queue.Put(static_cast<void*>(grpc_core::New<WorkItem>(i)));
+  }
+  // Queue should not have been expanded at this time.
+  GPR_ASSERT(queue.num_nodes() == queue.init_num_nodes());
+  for (int i = 0; i < queue.init_num_nodes(); ++i) {
+    WorkItem* item = static_cast<WorkItem*>(queue.Get());
+    queue.Put(item);
+  }
+  GPR_ASSERT(queue.num_nodes() == queue.init_num_nodes());
+  for (int i = 0; i < queue.init_num_nodes(); ++i) {
+    WorkItem* item = static_cast<WorkItem*>(queue.Get());
+    grpc_core::Delete(item);
+  }
+  // Queue never shrinks even it is empty.
+  GPR_ASSERT(queue.num_nodes() == queue.init_num_nodes());
+  GPR_ASSERT(queue.count() == 0);
+  // queue empty now
+  for (int i = 0; i < queue.init_num_nodes() * 2; ++i) {
+    queue.Put(static_cast<void*>(grpc_core::New<WorkItem>(i)));
+  }
+  GPR_ASSERT(queue.count() == queue.init_num_nodes() * 2);
+  // Queue should have been expanded once.
+  GPR_ASSERT(queue.num_nodes() == queue.init_num_nodes() * 2);
+  for (int i = 0; i < queue.init_num_nodes(); ++i) {
+    WorkItem* item = static_cast<WorkItem*>(queue.Get());
+    grpc_core::Delete(item);
+  }
+  GPR_ASSERT(queue.count() == queue.init_num_nodes());
+  // Queue will never shrink, should keep same number of node as before.
+  GPR_ASSERT(queue.num_nodes() == queue.init_num_nodes() * 2);
+  for (int i = 0; i < queue.init_num_nodes() + 1; ++i) {
+    queue.Put(static_cast<void*>(grpc_core::New<WorkItem>(i)));
+  }
+  GPR_ASSERT(queue.count() == queue.init_num_nodes() * 2 + 1);
+  // Queue should have been expanded twice.
+  GPR_ASSERT(queue.num_nodes() == queue.init_num_nodes() * 4);
+  for (int i = 0; i < queue.init_num_nodes() * 2 + 1; ++i) {
+    WorkItem* item = static_cast<WorkItem*>(queue.Get());
+    grpc_core::Delete(item);
+  }
+  GPR_ASSERT(queue.count() == 0);
+  GPR_ASSERT(queue.num_nodes() == queue.init_num_nodes() * 4);
+  gpr_log(GPR_DEBUG, "Done.");
+}
+
 static void test_many_thread(void) {
   gpr_log(GPR_INFO, "test_many_thread");
   const int num_producer_threads = 10;
@@ -172,6 +223,7 @@ int main(int argc, char** argv) {
   grpc::testing::TestEnvironment env(argc, argv);
   grpc_init();
   test_FIFO();
+  test_space_efficiency();
   test_many_thread();
   grpc_shutdown();
   return 0;