duckstation

metal_stream_buffer.mm (8243B)

---

 // SPDX-FileCopyrightText: 2023 Connor McLaughlin <stenzek@gmail.com>
 // SPDX-License-Identifier: (GPL-3.0 OR CC-BY-NC-ND-4.0)
 
 #include "metal_stream_buffer.h"
 #include "metal_device.h"
 
 #include "common/align.h"
 #include "common/assert.h"
 #include "common/log.h"
 
 Log_SetChannel(MetalDevice);
 
 MetalStreamBuffer::MetalStreamBuffer() = default;
 
 MetalStreamBuffer::~MetalStreamBuffer()
 {
   if (IsValid())
     Destroy();
 }
 
 bool MetalStreamBuffer::Create(id<MTLDevice> device, u32 size)
 {
   @autoreleasepool
   {
     const MTLResourceOptions options = MTLResourceStorageModeShared | MTLResourceCPUCacheModeWriteCombined;
 
     id<MTLBuffer> new_buffer = [device newBufferWithLength:size options:options];
     if (new_buffer == nil)
     {
       ERROR_LOG("Failed to create buffer.");
       return false;
     }
 
     if (IsValid())
       Destroy();
 
     // Replace with the new buffer
     m_size = size;
     m_current_offset = 0;
     m_current_gpu_position = 0;
     m_tracked_fences.clear();
     m_buffer = [new_buffer retain];
     m_host_pointer = static_cast<u8*>([new_buffer contents]);
     return true;
   }
 }
 
 void MetalStreamBuffer::Destroy()
 {
   m_size = 0;
   m_current_offset = 0;
   m_current_gpu_position = 0;
   m_tracked_fences.clear();
   [m_buffer release];
   m_buffer = nil;
   m_host_pointer = nullptr;
 }
 
 bool MetalStreamBuffer::ReserveMemory(u32 num_bytes, u32 alignment)
 {
   const u32 required_bytes = num_bytes + alignment;
 
   // Check for sane allocations
   if (required_bytes > m_size) [[unlikely]]
   {
     ERROR_LOG("Attempting to allocate {} bytes from a {} byte stream buffer", num_bytes, m_size);
     Panic("Stream buffer overflow");
     return false;
   }
 
   UpdateGPUPosition();
 
   // Is the GPU behind or up to date with our current offset?
   if (m_current_offset >= m_current_gpu_position)
   {
     const u32 remaining_bytes = m_size - m_current_offset;
     if (required_bytes <= remaining_bytes)
     {
       // Place at the current position, after the GPU position.
       m_current_offset = Common::AlignUp(m_current_offset, alignment);
       m_current_space = m_size - m_current_offset;
       return true;
     }
 
     // Check for space at the start of the buffer
     // We use < here because we don't want to have the case of m_current_offset ==
     // m_current_gpu_position. That would mean the code above would assume the
     // GPU has caught up to us, which it hasn't.
     if (required_bytes < m_current_gpu_position)
     {
       // Reset offset to zero, since we're allocating behind the gpu now
       m_current_offset = 0;
       m_current_space = m_current_gpu_position - 1;
       return true;
     }
   }
 
   // Is the GPU ahead of our current offset?
   if (m_current_offset < m_current_gpu_position)
   {
     // We have from m_current_offset..m_current_gpu_position space to use.
     const u32 remaining_bytes = m_current_gpu_position - m_current_offset;
     if (required_bytes < remaining_bytes)
     {
       // Place at the current position, since this is still behind the GPU.
       m_current_offset = Common::AlignUp(m_current_offset, alignment);
       m_current_space = m_current_gpu_position - m_current_offset - 1;
       return true;
     }
   }
 
   // Can we find a fence to wait on that will give us enough memory?
   if (WaitForClearSpace(required_bytes))
   {
     const u32 align_diff = Common::AlignUp(m_current_offset, alignment) - m_current_offset;
     m_current_offset += align_diff;
     m_current_space -= align_diff;
     return true;
   }
 
   // We tried everything we could, and still couldn't get anything. This means that too much space
   // in the buffer is being used by the command buffer currently being recorded. Therefore, the
   // only option is to execute it, and wait until it's done.
   return false;
 }
 
 void MetalStreamBuffer::CommitMemory(u32 final_num_bytes)
 {
   DebugAssert((m_current_offset + final_num_bytes) <= m_size);
   DebugAssert(final_num_bytes <= m_current_space);
 
   m_current_offset += final_num_bytes;
   m_current_space -= final_num_bytes;
   UpdateCurrentFencePosition();
 }
 
 void MetalStreamBuffer::UpdateCurrentFencePosition()
 {
   // Has the offset changed since the last fence?
   const u64 counter = MetalDevice::GetInstance().GetCurrentFenceCounter();
   if (!m_tracked_fences.empty() && m_tracked_fences.back().first == counter)
   {
     // Still haven't executed a command buffer, so just update the offset.
     m_tracked_fences.back().second = m_current_offset;
     return;
   }
 
   // New buffer, so update the GPU position while we're at it.
   m_tracked_fences.emplace_back(counter, m_current_offset);
 }
 
 void MetalStreamBuffer::UpdateGPUPosition()
 {
   auto start = m_tracked_fences.begin();
   auto end = start;
 
   const u64 completed_counter = MetalDevice::GetInstance().GetCompletedFenceCounter();
   while (end != m_tracked_fences.end() && completed_counter >= end->first)
   {
     m_current_gpu_position = end->second;
     ++end;
   }
 
   if (start != end)
   {
     m_tracked_fences.erase(start, end);
     if (m_current_offset == m_current_gpu_position)
     {
       // GPU is all caught up now.
       m_current_offset = 0;
       m_current_gpu_position = 0;
       m_current_space = m_size;
     }
   }
 }
 
 bool MetalStreamBuffer::WaitForClearSpace(u32 num_bytes)
 {
   u32 new_offset = 0;
   u32 new_space = 0;
   u32 new_gpu_position = 0;
 
   auto iter = m_tracked_fences.begin();
   for (; iter != m_tracked_fences.end(); ++iter)
   {
     // Would this fence bring us in line with the GPU?
     // This is the "last resort" case, where a command buffer execution has been forced
     // after no additional data has been written to it, so we can assume that after the
     // fence has been signaled the entire buffer is now consumed.
     u32 gpu_position = iter->second;
     if (m_current_offset == gpu_position)
     {
       new_offset = 0;
       new_space = m_size;
       new_gpu_position = 0;
       break;
     }
 
     // Assuming that we wait for this fence, are we allocating in front of the GPU?
     if (m_current_offset > gpu_position)
     {
       // This would suggest the GPU has now followed us and wrapped around, so we have from
       // m_current_position..m_size free, as well as and 0..gpu_position.
       const u32 remaining_space_after_offset = m_size - m_current_offset;
       if (remaining_space_after_offset >= num_bytes)
       {
         // Switch to allocating in front of the GPU, using the remainder of the buffer.
         new_offset = m_current_offset;
         new_space = m_size - m_current_offset;
         new_gpu_position = gpu_position;
         break;
       }
 
       // We can wrap around to the start, behind the GPU, if there is enough space.
       // We use > here because otherwise we'd end up lining up with the GPU, and then the
       // allocator would assume that the GPU has consumed what we just wrote.
       if (gpu_position > num_bytes)
       {
         new_offset = 0;
         new_space = gpu_position - 1;
         new_gpu_position = gpu_position;
         break;
       }
     }
     else
     {
       // We're currently allocating behind the GPU. This would give us between the current
       // offset and the GPU position worth of space to work with. Again, > because we can't
       // align the GPU position with the buffer offset.
       u32 available_space_inbetween = gpu_position - m_current_offset;
       if (available_space_inbetween > num_bytes)
       {
         // Leave the offset as-is, but update the GPU position.
         new_offset = m_current_offset;
         new_space = available_space_inbetween - 1;
         new_gpu_position = gpu_position;
         break;
       }
     }
   }
 
   // Did any fences satisfy this condition?
   // Has the command buffer been executed yet? If not, the caller should execute it.
   MetalDevice& dev = MetalDevice::GetInstance();
   if (iter == m_tracked_fences.end() || iter->first == dev.GetCurrentFenceCounter())
     return false;
 
   // Wait until this fence is signaled. This will fire the callback, updating the GPU position.
   dev.WaitForFenceCounter(iter->first);
   m_tracked_fences.erase(m_tracked_fences.begin(), m_current_offset == iter->second ? m_tracked_fences.end() : ++iter);
   m_current_offset = new_offset;
   m_current_space = new_space;
   m_current_gpu_position = new_gpu_position;
   return true;
 }