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GPU.deviceInfo(): select the device like MLX, without the window server #498

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Merged
davidkoski merged 1 commit into from
Oct 20, 2026
Merged

GPU.deviceInfo(): select the device like MLX, without the window server #498

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20 changes: 18 additions & 2 deletions Source/MLX/GPU+Metal.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -242,13 +242,29 @@ public enum GPU {
}

/// Get information about the GPU device and system settings
///
/// The value is computed once per process.
public static func deviceInfo() -> DeviceInfo {
cachedDeviceInfo
}

private static let cachedDeviceInfo: DeviceInfo = {
var mib = [CTL_HW, HW_MEMSIZE]
var memSize: size_t = 0
var length: size_t = MemoryLayout.size(ofValue: memSize)
sysctl(&mib, 2, &memSize, &length, nil, 0)

if let device = MTLCreateSystemDefaultDevice() {
// Select the device the same way as MLX (metal::load_device): the first
// device of MTLCopyAllDevices(), else the system default device. In a
// command-line process MTLCreateSystemDefaultDevice() opens a window
// server session, which can stall for several seconds.
#if os(macOS)

@davidkoski davidkoski Oct 15, 2026

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You might also want to cover macCatalyst here too -- the same calls are available but it isn't os(macOS):

#if os(macOS) || targetEnvironment(macCatalyst)

Though if the primary concern is for command line tools, I am not sure you can create one that is macCatalyst.

let device = MTLCopyAllDevices().first ?? MTLCreateSystemDefaultDevice()
#else
let device = MTLCreateSystemDefaultDevice()
#endif

if let device {
let architecture: String
if #available(macOS 14.0, iOS 17.0, tvOS 17.0, *) {
architecture = device.architecture.name
Expand All @@ -265,5 +281,5 @@ public enum GPU {
architecture: "Unknown", maxBufferSize: 0, maxRecommendedWorkingSetSize: 0,
memorySize: memSize)
}
}
}()
}
15 changes: 15 additions & 0 deletions Tests/MLXTests/MemoryTests.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -12,4 +12,19 @@ class MemoryTests: XCTestCase {
print(x * x)
}
}

func testDeviceInfo() {
let info = GPU.deviceInfo()
XCTAssertGreaterThan(info.memorySize, 0)

guard Device.defaultDevice().deviceType == .gpu else { return }
XCTAssertNotEqual(info.architecture, "Unknown")
XCTAssertGreaterThan(info.maxBufferSize, 0)
XCTAssertGreaterThan(info.maxRecommendedWorkingSetSize, 0)

let again = GPU.deviceInfo()
XCTAssertEqual(again.architecture, info.architecture)
XCTAssertEqual(again.maxBufferSize, info.maxBufferSize)
XCTAssertEqual(again.maxRecommendedWorkingSetSize, info.maxRecommendedWorkingSetSize)
}
}
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