intern/ghost/intern/GHOST_ContextCGL.hh

@@ -138,7 +138,6 @@ class GHOST_ContextCGL : public GHOST_Context {
   bool m_useMetalForRendering = false;
   NSView *m_metalView;
   CAMetalLayer *m_metalLayer;
-  MTLCommandQueue *m_metalCmdQueue;
   MTLRenderPipelineState *m_metalRenderPipeline;
   bool m_ownsMetalDevice;
 
@@ -182,6 +181,9 @@ class GHOST_ContextCGL : public GHOST_Context {
   static NSOpenGLContext *s_sharedOpenGLContext;
   static int s_sharedCount;
 
+  /* Single device queue for multiple contexts. */
+  static MTLCommandQueue *s_sharedMetalCommandQueue;
+
   /* Metal functions */
   void metalInit();
   void metalFree();

intern/ghost/intern/GHOST_ContextCGL.mm

@@ -43,6 +43,7 @@ static void ghost_fatal_error_dialog(const char *msg)
 }
 
 NSOpenGLContext *GHOST_ContextCGL::s_sharedOpenGLContext = nil;
+MTLCommandQueue *GHOST_ContextCGL::s_sharedMetalCommandQueue = nil;
 int GHOST_ContextCGL::s_sharedCount = 0;
 
 GHOST_ContextCGL::GHOST_ContextCGL(bool stereoVisual,
@@ -54,7 +55,6 @@ GHOST_ContextCGL::GHOST_ContextCGL(bool stereoVisual,
       m_useMetalForRendering(type == GHOST_kDrawingContextTypeMetal),
       m_metalView(metalView),
       m_metalLayer(metalLayer),
-      m_metalCmdQueue(nil),
       m_metalRenderPipeline(nil),
       m_openGLView(openGLView),
       m_openGLContext(nil),
@@ -318,7 +318,7 @@ id<MTLTexture> GHOST_ContextCGL::metalOverlayTexture()
 
 MTLCommandQueue *GHOST_ContextCGL::metalCommandQueue()
 {
-  return m_metalCmdQueue;
+  return s_sharedMetalCommandQueue;
 }
 MTLDevice *GHOST_ContextCGL::metalDevice()
 {
@@ -530,10 +530,14 @@ void GHOST_ContextCGL::metalInit()
     /* clang-format on */
     id<MTLDevice> device = m_metalLayer.device;
 
-    /* Create a command queue for blit/present operation. */
-    m_metalCmdQueue = (MTLCommandQueue *)[device
-        newCommandQueueWithMaxCommandBufferCount:GHOST_ContextCGL::max_command_buffer_count];
-    [m_metalCmdQueue retain];
+    /* Create a command queue for blit/present operation. Note: All context should share a single
+     * command queue to ensure correct ordering of work submitted from multiple contexts. */
+    if (s_sharedMetalCommandQueue == nil) {
+      s_sharedMetalCommandQueue = (MTLCommandQueue *)[device
+          newCommandQueueWithMaxCommandBufferCount:GHOST_ContextCGL::max_command_buffer_count];
+    }
+    /* Ensure active GHOSTContext retains a reference to the shared context. */
+    [s_sharedMetalCommandQueue retain];
 
     /* Create shaders for blit operation. */
     NSString *source = @R"msl(
@@ -616,9 +620,6 @@ void GHOST_ContextCGL::metalInit()
 
 void GHOST_ContextCGL::metalFree()
 {
-  if (m_metalCmdQueue) {
-    [m_metalCmdQueue release];
-  }
   if (m_metalRenderPipeline) {
     [m_metalRenderPipeline release];
   }
@@ -789,7 +790,7 @@ void GHOST_ContextCGL::metalUpdateFramebuffer()
         overlayTex;  //[(MTLTexture *)overlayTex retain];
 
     /* Clear texture on create */
-    id<MTLCommandBuffer> cmdBuffer = [m_metalCmdQueue commandBuffer];
+    id<MTLCommandBuffer> cmdBuffer = [s_sharedMetalCommandQueue commandBuffer];
     MTLRenderPassDescriptor *passDescriptor = [MTLRenderPassDescriptor renderPassDescriptor];
     {
       auto attachment = [passDescriptor.colorAttachments objectAtIndexedSubscript:0];
@@ -854,7 +855,7 @@ void GHOST_ContextCGL::metalSwapBuffers()
     }
 
     if (!m_useMetalForRendering) {
-      id<MTLCommandBuffer> cmdBuffer = [m_metalCmdQueue commandBuffer];
+      id<MTLCommandBuffer> cmdBuffer = [s_sharedMetalCommandQueue commandBuffer];
       {
         assert(m_defaultFramebufferMetalTexture[current_swapchain_index].texture != nil);
         id<MTLRenderCommandEncoder> enc = [cmdBuffer
@@ -896,7 +897,7 @@ void GHOST_ContextCGL::initClear()
 #if WITH_METAL
     // TODO (mg_gpusw_apple) this path is never taken, this is legacy left from inital integration
     // of metal and gl, the whole file should be cleaned up and stripped of the legacy path
-    id<MTLCommandBuffer> cmdBuffer = [m_metalCmdQueue commandBuffer];
+    id<MTLCommandBuffer> cmdBuffer = [s_sharedMetalCommandQueue commandBuffer];
     MTLRenderPassDescriptor *passDescriptor = [MTLRenderPassDescriptor renderPassDescriptor];
     {
       auto attachment = [passDescriptor.colorAttachments objectAtIndexedSubscript:0];

source/blender/gpu/metal/mtl_command_buffer.mm

@@ -17,13 +17,6 @@ using namespace blender::gpu;
 
 namespace blender::gpu {
 
-/* Global sync event used across MTLContext's.
- * This resolves flickering artifacts from command buffer
- * dependencies not being honored for work submitted between
- * different GPUContext's. */
-id<MTLEvent> MTLCommandBufferManager::sync_event = nil;
-uint64_t MTLCommandBufferManager::event_signal_val = 0;
-
 /* Counter for active command buffers. */
 int MTLCommandBufferManager::num_active_cmd_bufs = 0;
 
@@ -76,11 +69,6 @@ id<MTLCommandBuffer> MTLCommandBufferManager::ensure_begin()
     [active_command_buffer_ retain];
     MTLCommandBufferManager::num_active_cmd_bufs++;
 
-    /* Ensure command buffers execute in submission order across multiple MTLContext's. */
-    if (this->sync_event != nil) {
-      [active_command_buffer_ encodeWaitForEvent:this->sync_event value:this->event_signal_val];
-    }
-
     /* Ensure we begin new Scratch Buffer if we are on a new frame. */
     MTLScratchBufferManager &mem = context_.memory_manager;
     mem.ensure_increment_scratch_buffer();
@@ -108,20 +96,6 @@ bool MTLCommandBufferManager::submit(bool wait)
   context_.memory_manager.flush_active_scratch_buffer();
 
   /*** Submit Command Buffer. ***/
-  /* Strict ordering ensures command buffers are guaranteed to execute after a previous
-   * one has completed. Resolves flickering when command buffers are submitted from
-   * different MTLContext's. */
-  if (MTLCommandBufferManager::sync_event == nil) {
-    MTLCommandBufferManager::sync_event = [context_.device newEvent];
-    BLI_assert(MTLCommandBufferManager::sync_event);
-    [MTLCommandBufferManager::sync_event retain];
-  }
-  BLI_assert(MTLCommandBufferManager::sync_event != nil);
-  MTLCommandBufferManager::event_signal_val++;
-
-  [active_command_buffer_ encodeSignalEvent:MTLCommandBufferManager::sync_event
-                                      value:MTLCommandBufferManager::event_signal_val];
-
   /* Command buffer lifetime tracking. */
   /* Increment current MTLSafeFreeList reference counter to flag MTLBuffers freed within
    * the current command buffer lifetime as used.

source/blender/gpu/metal/mtl_context.hh

@@ -536,10 +536,6 @@ class MTLCommandBufferManager {
   friend class MTLContext;
 
  public:
-  /* Event to coordinate sequential execution across all "main" command buffers. */
-  static id<MTLEvent> sync_event;
-  static uint64_t event_signal_val;
-
   /* Counter for active command buffers. */
   static int num_active_cmd_bufs;
 

source/blender/gpu/metal/mtl_state.mm

@@ -608,19 +608,6 @@ void MTLFence::wait()
     return;
   }
 
-  /* Note(#106431 #106704): `sync_event` is a global cross-context synchronization primitive used
-   * to ensure GPU workloads execute in the correct order across contexts.
-   *
-   * To prevent unexpected GPU stalls, this needs to be reset when used along side explicit
-   * synchronization. Previously this was handled during frame boundaries, however, to eliminate
-   * situational flickering (#106704), only reset this during the cases where we are waiting on
-   * synchronization primitives. */
-  if (MTLCommandBufferManager::sync_event != nil) {
-    [MTLCommandBufferManager::sync_event release];
-    MTLCommandBufferManager::sync_event = nil;
-    MTLCommandBufferManager::event_signal_val = 0;
-  }
-
   if (signalled_) {
     MTLContext *ctx = MTLContext::get();
     BLI_assert(ctx);