From 8a7be0a747e047bd09379cc8effa0d809ba81443 Mon Sep 17 00:00:00 2001
From: nimlgen <138685161+nimlgen@users.noreply.github.com>
Date: Tue, 12 Aug 2025 16:16:34 +0300
Subject: [PATCH] metal: workaround for transfers sync issue (#11622)

* metal: workaround for transfers sync issue

* metal tracsfer sync is broken

* hm

* rm it?

* keep it
---
 tinygrad/runtime/ops_metal.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tinygrad/runtime/ops_metal.py b/tinygrad/runtime/ops_metal.py
index 027e5080ab..9e453eb729 100644
--- a/tinygrad/runtime/ops_metal.py
+++ b/tinygrad/runtime/ops_metal.py
@@ -221,6 +221,9 @@ class MetalAllocator(LRUAllocator[MetalDevice]):
     msg("setLabel:")(src_command_buffer, to_ns_str(f"COPY {src_dev.device} -> {dest_dev.device}"))
     msg("commit")(src_command_buffer)
     src_dev.mtl_buffers_in_flight.append(src_command_buffer)
+    # Transfers currently synchronize the completion. Otherwise, copies can sometimes lead to incorrect values.
+    # There is no real metal multidevice support for now, so transfer is used only for tests.
+    src_dev.synchronize()
   def _cp_mv(self, dst, src, prof_desc):
     with cpu_profile(prof_desc, self.dev.device, is_copy=True): dst[:] = src
   def _as_buffer(self, src:MetalBuffer) -> memoryview: