Rendering into multiple views with Metal

Question

I have successfully used Metal to render into a simple view, and update at full FPS, by following and modifying the code at https://github.com/jim-ec/metal-hello-triangle

I am now trying to repeat the process by drawing into multiple views in an NSCollectionView.

My render code is as follows, where each view in the NSCollectionView has a global Renderer object as its delegate:

class Renderer {

/// Initialisation as per the linked tutorial

public func draw(in view: MTKView)
{
    let dataSize     = VERTEX_DATA.count * MemoryLayout.size(ofValue: VERTEX_DATA[0])
    VERTEX_DATA[1][1] = Float(arc4random_uniform(100)) / 100
    let vertexBuffer = view.device?.makeBuffer(bytes:   VERTEX_DATA,
                                              length:  dataSize,
                                              options: [])

    let commandBuffer  = mCommandQueue.makeCommandBuffer()!

    let commandEncoder = commandBuffer.makeRenderCommandEncoder(descriptor: view.currentRenderPassDescriptor!)
    commandEncoder?.setRenderPipelineState(mPipeline)
    commandEncoder?.setVertexBuffer(vertexBuffer, offset: 0, index: 0)
    commandEncoder?.drawPrimitives(type: .triangle,
                                 vertexStart: 0,
                                 vertexCount: 3,
                                 instanceCount: 1)
    commandEncoder?.endEncoding()

    commandBuffer.present(view.currentDrawable!)
    commandBuffer.commit()
    commandBuffer.waitUntilCompleted()
}

}

The arc4random_uniform call is to make the triangles change colour, so I can confirm that they are redrawing.

Unfortunately, views only update around 3 times a second, and not at all in sync. Looking at instruments, the GPU is barely breaking a sweat, and the CPU overhead of both WindowServer and my app are pretty huge. The draw function is now very heavy with makeRenderCommandEncoder becoming a real bottleneck, and there are obviously some synchronisation issues given the sporadic updating.

I expected this to be more-or-less similar performance as I'm still doing a trivial amount of drawing, but it really isn't. What am I doing wrong?

Working example available at https://github.com/SirWhiteHat/MetalPerformanceProblem

Thank you!