# sampleCounters(sampleBuffer:sampleIndex:barrier:) Encodes a command to sample hardware counters, providing performance information. ``` func sampleCounters(sampleBuffer: any MTLCounterSampleBuffer, sampleIndex: Int, barrier: Bool) ``` ## Parameters `sampleBuffer` An [`MTLCounterSampleBuffer`](/documentation/Metal/MTLCounterSampleBuffer) instance that stores the GPU hardware data. `sampleIndex` An index within `sampleBuffer` the command stores the data to. `barrier` Whether or not the command inserts a barrier before sampling the counter’s data. A barrier ensures that the commands you encode before this one complete before the GPU samples the hardware counters, but can negatively impact runtime performance. Running this command without a barrier means the GPU can sample counters concurrently with other commands from the encoder. The `barrier` parameter for the command has no impact on sampling commands from other passes. ## Discussion> Important: > To use a sample buffer, it needs to be part of the ``doc://com.apple.metal/documentation/Metal/MTLComputePassDescriptor/sampleBufferAttachments`` on the compute pass descriptor. See [GPU counters and counter sample buffers](/documentation/Metal/gpu-counters-and-counter-sample-buffers), [Sampling GPU data into counter sample buffers](/documentation/Metal/sampling-gpu-data-into-counter-sample-buffers), and [`MTLCounter`](/documentation/Metal/MTLCounter) for more information. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)