Rewrite SamplingCircularQueue

src/circular-queue.cc

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 16 matching lines @@
 
 #include "v8.h"
 
 #include "circular-queue-inl.h"
 
 namespace v8 {
 namespace internal {
 
 
 SamplingCircularQueue::SamplingCircularQueue(size_t record_size_in_bytes,
-                                             size_t desired_chunk_size_in_bytes,
-                                             unsigned buffer_size_in_chunks)
-    : record_size_(record_size_in_bytes / sizeof(Cell)),
-      chunk_size_in_bytes_(desired_chunk_size_in_bytes / record_size_in_bytes *
-                        record_size_in_bytes + sizeof(Cell)),
-      chunk_size_(chunk_size_in_bytes_ / sizeof(Cell)),
-      buffer_size_(chunk_size_ * buffer_size_in_chunks),
-      buffer_(NewArray<Cell>(buffer_size_)) {
-  ASSERT(record_size_ * sizeof(Cell) == record_size_in_bytes);
-  ASSERT(chunk_size_ * sizeof(Cell) == chunk_size_in_bytes_);
-  ASSERT(buffer_size_in_chunks > 2);
-  // Mark all chunks as clear.
-  for (size_t i = 0; i < buffer_size_; i += chunk_size_) {
-    buffer_[i] = kClear;
+                                             unsigned buffer_size_in_records)
+    : entry_size_(RoundUp(record_size_in_bytes + sizeof(Cell),
+                  kProcessorCacheLineSize) / sizeof(Cell)),
+      buffer_size_(entry_size_ * buffer_size_in_records) {
+  const size_t cache_line_size = kProcessorCacheLineSize / sizeof(Cell);
+  not_aligned_buffer_ = NewArray<Cell>(buffer_size_ + cache_line_size);
+  // Align on cache line boundaries.
+  buffer_ = reinterpret_cast<Cell*>(RoundUp(not_aligned_buffer_,
+                                            cache_line_size));
+  // Mark all entries as empty.
+  for (size_t i = 0; i < buffer_size_; i += entry_size_) {
+    buffer_[i] = kEmpty;
   }
 
   // Layout producer and consumer position pointers each on their own
   // cache lines to avoid cache lines thrashing due to simultaneous
   // updates of positions by different processor cores.
   const int positions_size =
       RoundUp(1, kProcessorCacheLineSize) +
       RoundUp(static_cast<int>(sizeof(ProducerPosition)),
               kProcessorCacheLineSize) +
       RoundUp(static_cast<int>(sizeof(ConsumerPosition)),
               kProcessorCacheLineSize);
   positions_ = NewArray<byte>(positions_size);
 
   producer_pos_ = reinterpret_cast<ProducerPosition*>(
       RoundUp(positions_, kProcessorCacheLineSize));
-  producer_pos_->next_chunk_pos = buffer_;
   producer_pos_->enqueue_pos = buffer_;
 
   consumer_pos_ = reinterpret_cast<ConsumerPosition*>(
       reinterpret_cast<byte*>(producer_pos_) + kProcessorCacheLineSize);
   ASSERT(reinterpret_cast<byte*>(consumer_pos_ + 1) <=
          positions_ + positions_size);
-  consumer_pos_->dequeue_chunk_pos = buffer_;
-  // The distance ensures that producer and consumer never step on
-  // each other's chunks and helps eviction of produced data from
-  // the CPU cache (having that chunk size is bigger than the cache.)
-  const size_t producer_consumer_distance = (2 * chunk_size_);
-  consumer_pos_->dequeue_chunk_poll_pos = buffer_ + producer_consumer_distance;
-  consumer_pos_->dequeue_pos = NULL;
+  consumer_pos_->dequeue_pos = buffer_;
 }
 
 
 SamplingCircularQueue::~SamplingCircularQueue() {
   DeleteArray(positions_);
-  DeleteArray(buffer_);
+  DeleteArray(not_aligned_buffer_);
 }
 
 
 void* SamplingCircularQueue::StartDequeue() {
-  if (consumer_pos_->dequeue_pos != NULL) {
-    return consumer_pos_->dequeue_pos;
-  } else {
-    if (Acquire_Load(consumer_pos_->dequeue_chunk_poll_pos) != kClear) {
-      // Skip marker.
-      consumer_pos_->dequeue_pos = consumer_pos_->dequeue_chunk_pos + 1;
-      consumer_pos_->dequeue_end_pos =
-          consumer_pos_->dequeue_chunk_pos + chunk_size_;
-      return consumer_pos_->dequeue_pos;
-    } else {
-      return NULL;
-    }
+  MemoryBarrier();

[Benedikt Meurer, 2013/08/13 09:31:32]

Why do we need this memory barrier here?

[yurys, 2013/08/13 10:05:20]

Because we'd like to see up-to-date value at consumer_pos_->dequeue_pos and
Acquire_Load doesn't guarantee that we won't use some cached version of it.

+  if (Acquire_Load(consumer_pos_->dequeue_pos) != kEmpty) {
+    // Skip marker.
+    return consumer_pos_->dequeue_pos + 1;
   }
+  return NULL;
 }
 
 
 void SamplingCircularQueue::FinishDequeue() {
-  consumer_pos_->dequeue_pos += record_size_;
-  if (consumer_pos_->dequeue_pos < consumer_pos_->dequeue_end_pos) return;
-  // Move to next chunk.
-  consumer_pos_->dequeue_pos = NULL;
-  *consumer_pos_->dequeue_chunk_pos = kClear;
-  consumer_pos_->dequeue_chunk_pos += chunk_size_;
-  WrapPositionIfNeeded(&consumer_pos_->dequeue_chunk_pos);
-  consumer_pos_->dequeue_chunk_poll_pos += chunk_size_;
-  WrapPositionIfNeeded(&consumer_pos_->dequeue_chunk_poll_pos);
+  Release_Store(consumer_pos_->dequeue_pos, kEmpty);
+  consumer_pos_->dequeue_pos += entry_size_;
+  WrapPositionIfNeeded(&consumer_pos_->dequeue_pos);
 }

[Benedikt Meurer, 2013/08/13 09:31:32]

T* StartDequeue() {
  if (Acquire_Load(&buffer_[dequeue_pos_ + kRecordStateOffset] != kFull) return
NULL;
  return reinterpret_cast<T*>(&buffer_[dequeue_pos_]);
}

void FinishDequeue() {
  ASSERT(Release_Load(&buffer_[dequeue_pos_ + kRecordStateOffset] == kFull);
  Release_Store(&buffer_[dequeue_pos_ + kRecordStateOffset], kEmpty);
  dequeue_pos_ = (dequeue_pos + kRecordSize) % (N * kRecordSize);
}

[yurys, 2013/08/13 14:10:29]

Changed that code.

 
-
-void SamplingCircularQueue::FlushResidualRecords() {
-  // Eliminate producer / consumer distance.
-  consumer_pos_->dequeue_chunk_poll_pos = consumer_pos_->dequeue_chunk_pos;
-}
-
-
 } }  // namespace v8::internal