diff --git a/tinygrad/runtime/metal.py b/tinygrad/runtime/metal.py
index 486bd9ea24..007adf5ca0 100644
--- a/tinygrad/runtime/metal.py
+++ b/tinygrad/runtime/metal.py
@@ -3,6 +3,7 @@ import Metal # type: ignore
 import numpy as np
 from typing import List, Any
 from tinygrad.ops import DEBUG, GlobalCounters
+from tinygrad.helpers import prod
 
 device = Metal.MTLCreateSystemDefaultDevice()
 mtl_queue = device.newCommandQueue()
@@ -19,11 +20,7 @@ class CLImage:
 class CLBuffer:
   def __init__(self, size): self._cl = device.newBufferWithLength_options_(size, Metal.MTLResourceStorageModeShared)
   def copyin(self, b:np.ndarray):
-    # TODO: don't reallocate buffer!
-    self._cl = device.newBufferWithBytes_length_options_(
-      b.astype(np.float32).data,
-      b.size*4,
-      Metal.MTLResourceStorageModeShared)
+    np.copyto(np.frombuffer(self._cl.contents().as_buffer(self._cl.length()), dtype=np.float32), b.data)
 
   def toCPU(self):
     sync()
@@ -45,15 +42,19 @@ class CLProgram:
     self.library = device.newLibraryWithSource_options_error_(prg, options, None)
     assert self.library[0] is not None, str(self.library)
     self.fxn = self.library[0].newFunctionWithName_(name)
+    self.pipeline_state = device.newComputePipelineStateWithFunction_error_(self.fxn, None)
+    assert self.pipeline_state[0] is not None, str(self.pipeline_state)
+
   def __call__(self, global_size, local_size, *args):
     global_size += [1] * (3-len(global_size))
     if local_size is None: local_size = [32]
     local_size += [1] * (3-len(local_size))
-    pipeline_state = device.newComputePipelineStateWithFunction_error_(self.fxn, None)
-    assert pipeline_state[0] is not None, str(pipeline_state)
+
+    assert prod(local_size) <= self.pipeline_state[0].maxTotalThreadsPerThreadgroup(), f"local size {local_size} bigger than {self.pipeline_state[0].maxTotalThreadsPerThreadgroup()} with exec width {self.pipeline_state[0].threadExecutionWidth()} memory length {self.pipeline_state[0].staticThreadgroupMemoryLength()}"
     command_buffer = mtl_queue.commandBuffer()
     encoder = command_buffer.computeCommandEncoder()
-    encoder.setComputePipelineState_(pipeline_state[0])
+    
+    encoder.setComputePipelineState_(self.pipeline_state[0])
     for i,a in enumerate(args):
       encoder.setBuffer_offset_atIndex_(a, 0, i)
     encoder.dispatchThreads_threadsPerThreadgroup_(Metal.MTLSize(*global_size), Metal.MTLSize(*local_size))