[dxvk] Implement thread-safe buffer renaming

This is required for resource mapping on deferred contexts.
May also fix a potential synchronization issue where a buffer
could be mapped multiple times before the CS thread would mark
the physical buffer as used, which would result in invalid data.

src/dxvk/dxvk_buffer.cpp

@@ -15,44 +15,49 @@ namespace dxvk {
     m_physSliceLength = createInfo.size;
     m_physSliceStride = align(createInfo.size, 256);
     
-    // Initialize a single backing bufer with one slice
-    m_physBuffers[0] = this->allocPhysicalBuffer(1);
-    m_physSlice      = this->allocPhysicalSlice();
+    // Allocate a single buffer slice
+    m_physSlice = this->allocPhysicalBuffer(1)
+      ->slice(0, m_physSliceStride);
   }
   
   
-  void DxvkBuffer::rename(const DxvkPhysicalBufferSlice& slice) {
+  DxvkPhysicalBufferSlice DxvkBuffer::rename(const DxvkPhysicalBufferSlice& slice) {
+    DxvkPhysicalBufferSlice prevSlice = std::move(m_physSlice);
+    
     m_physSlice = slice;
     m_revision += 1;
+    return prevSlice;
   }
   
   
   DxvkPhysicalBufferSlice DxvkBuffer::allocPhysicalSlice() {
-    if (m_physSliceId >= m_physSliceCount) {
-      m_physBufferId = (m_physBufferId + 1) % m_physBuffers.size();
-      m_physSliceId  = 0;
+    std::unique_lock<std::mutex> lock(m_mutex);
+    
+    // If necessary, create a new buffer
+    // that we'll allocate slices from.
+    if (m_slices.size() == 0) {
+      const Rc<DxvkPhysicalBuffer> buffer
+        = this->allocPhysicalBuffer(m_physSliceCount);
       
-      if (m_physBuffers[m_physBufferId] == nullptr) {
-        // Make sure that all buffers have the same size. If we don't do this,
-        // one of the physical buffers may grow indefinitely while the others
-        // remain small, depending on the usage pattern of the application.
-        m_physBuffers[m_physBufferId] = this->allocPhysicalBuffer(m_physSliceCount);
-      } else if (m_physBuffers[m_physBufferId]->isInUse()) {
-        // Allocate a new physical buffer if the current one is still in use.
-        // This also indicates that the buffer gets updated frequently, so we
-        // will double the size of the physical buffers to accomodate for it.
-        if (m_physBufferId == 0) {
-          std::fill(m_physBuffers.begin(), m_physBuffers.end(), nullptr);
-          m_physSliceCount *= 2;
-        }
-        
-        m_physBuffers[m_physBufferId] = this->allocPhysicalBuffer(m_physSliceCount);
+      for (uint32_t i = 0; i < m_physSliceCount; i++) {
+        m_slices.push_back(buffer->slice(
+          m_physSliceStride * i,
+          m_physSliceLength));
       }
+      
+      m_physSliceCount *= 2;
     }
     
-    return m_physBuffers[m_physBufferId]->slice(
-      m_physSliceStride * m_physSliceId++,
-      m_physSliceLength);
+    // Take the first slice from the queue
+    DxvkPhysicalBufferSlice result = std::move(m_slices.back());
+    m_slices.pop_back();
+    return result;
+  }
+  
+  
+  void DxvkBuffer::freePhysicalSlice(const DxvkPhysicalBufferSlice& slice) {
+    std::unique_lock<std::mutex> lock(m_mutex);
+    m_slices.push_back(slice);
   }
   
   
@@ -93,4 +98,23 @@ namespace dxvk {
       m_vkd, m_buffer->slice(), m_info);
   }
   
+  
+  DxvkBufferTracker:: DxvkBufferTracker() { }
+  DxvkBufferTracker::~DxvkBufferTracker() { }
+  
+  
+  void DxvkBufferTracker::freeBufferSlice(
+    const Rc<DxvkBuffer>&           buffer,
+    const DxvkPhysicalBufferSlice&  slice) {
+    m_entries.push_back({ buffer, slice });
+  }
+  
+  
+  void DxvkBufferTracker::reset() {
+    for (const auto& e : m_entries)
+      e.buffer->freePhysicalSlice(e.slice);
+      
+    m_entries.clear();
+  }
+  
 }

src/dxvk/dxvk_buffer.h

@@ -1,5 +1,8 @@
 #pragma once
 
+#include <mutex>
+#include <vector>
+
 #include "dxvk_buffer_res.h"
 
 namespace dxvk {
@@ -106,41 +109,50 @@ namespace dxvk {
      * not call this directly as this is called implicitly
      * by the context's \c invalidateBuffer method.
      * \param [in] slice The new backing resource
+     * \returns Previous buffer slice
      */
-    void rename(
+    DxvkPhysicalBufferSlice rename(
       const DxvkPhysicalBufferSlice& slice);
     
     /**
      * \brief Allocates new physical resource
-     * 
-     * This method must not be called from multiple threads
-     * simultaneously, but it can be called in parallel with
-     * \ref rename and other methods of this class.
      * \returns The new backing buffer slice
      */
     DxvkPhysicalBufferSlice allocPhysicalSlice();
     
+    /**
+     * \brief Frees a physical buffer slice
+     * 
+     * Marks the slice as free so that it can be used for
+     * subsequent allocations. Called automatically when
+     * the slice is no longer needed by the GPU.
+     * \param [in] slice The buffer slice to free
+     */
+    void freePhysicalSlice(
+      const DxvkPhysicalBufferSlice& slice);
+    
   private:
     
     DxvkDevice*             m_device;
     DxvkBufferCreateInfo    m_info;
     VkMemoryPropertyFlags   m_memFlags;
+    
     DxvkPhysicalBufferSlice m_physSlice;
     uint32_t                m_revision = 0;
     
-    // TODO maybe align this to a cache line in order
-    // to avoid false sharing once CSMT is implemented
-    VkDeviceSize m_physBufferId     = 0;
-    VkDeviceSize m_physSliceId      = 0;
-    VkDeviceSize m_physSliceCount   = 1;
+    std::mutex                           m_mutex;
+    std::vector<DxvkPhysicalBufferSlice> m_slices;
+    
     VkDeviceSize m_physSliceLength  = 0;
     VkDeviceSize m_physSliceStride  = 0;
-    
-    std::array<Rc<DxvkPhysicalBuffer>, 2> m_physBuffers;
+    VkDeviceSize m_physSliceCount   = 2;
     
     Rc<DxvkPhysicalBuffer> allocPhysicalBuffer(
             VkDeviceSize    sliceCount) const;
     
+    void lock();
+    void unlock();
+    
   };
   
   
@@ -360,4 +372,36 @@ namespace dxvk {
     
   };
   
+  
+  /**
+   * \brief Buffer slice tracker
+   * 
+   * Stores a list of buffer slices that can be
+   * freed. Useful when buffers have been renamed
+   * and the original slice is no longer needed.
+   */
+  class DxvkBufferTracker {
+    
+  public:
+    
+    DxvkBufferTracker();
+    ~DxvkBufferTracker();
+    
+    void freeBufferSlice(
+      const Rc<DxvkBuffer>&           buffer,
+      const DxvkPhysicalBufferSlice&  slice);
+    
+    void reset();
+    
+  private:
+    
+    struct Entry {
+      Rc<DxvkBuffer>          buffer;
+      DxvkPhysicalBufferSlice slice;
+    };
+    
+    std::vector<Entry> m_entries;
+    
+  };
+  
 }

src/dxvk/dxvk_cmdlist.cpp

@@ -82,6 +82,8 @@ namespace dxvk {
   
   
   void DxvkCommandList::reset() {
+    m_bufferTracker.reset();
+    m_eventTracker.reset();
     m_queryTracker.reset();
     m_stagingAlloc.reset();
     m_descAlloc.reset();

src/dxvk/dxvk_cmdlist.h

@@ -3,6 +3,7 @@
 #include <unordered_set>
 
 #include "dxvk_binding.h"
+#include "dxvk_buffer.h"
 #include "dxvk_descriptor.h"
 #include "dxvk_event_tracker.h"
 #include "dxvk_lifetime.h"
@@ -62,6 +63,21 @@ namespace dxvk {
      */
     void endRecording();
     
+    /**
+     * \brief Frees physical buffer slice
+     * 
+     * After the command buffer execution has finished,
+     * the given physical slice will be released to the
+     * virtual buffer object so that it can be reused.
+     * \param [in] buffer The virtual buffer object
+     * \param [in] slice The physical buffer slice
+     */
+    void freePhysicalBufferSlice(
+      const Rc<DxvkBuffer>&           buffer,
+      const DxvkPhysicalBufferSlice&  slice) {
+      m_bufferTracker.freeBufferSlice(buffer, slice);
+    }
+    
     /**
      * \brief Adds a resource to track
      * 
@@ -509,6 +525,7 @@ namespace dxvk {
     DxvkStagingAlloc    m_stagingAlloc;
     DxvkQueryTracker    m_queryTracker;
     DxvkEventTracker    m_eventTracker;
+    DxvkBufferTracker   m_bufferTracker;
     
   };
   

src/dxvk/dxvk_context.cpp

@@ -888,7 +888,8 @@ namespace dxvk {
     const Rc<DxvkBuffer>&           buffer,
     const DxvkPhysicalBufferSlice&  slice) {
     // Allocate new backing resource
-    buffer->rename(slice);
+    DxvkPhysicalBufferSlice prevSlice = buffer->rename(slice);
+    m_cmd->freePhysicalBufferSlice(buffer, prevSlice);
     
     // We also need to update all bindings that the buffer
     // may be bound to either directly or through views.