Scroll hitches

Scroll hitches:

When a rendered frame does not end up on-screen at its expected time

• Hitch Time: Time in ms that a frame is late to display
• Hitch Ratio: Hitch time in ms per second for a given duration

Catch Hitches using Performance XCTests

Xcode11 introduce XCTMatric, which can gather metrics during performance tests.

Inside it, XCTOSSignpostMetric is a metric to record the time a performance tests spends executing a signposted region of code.

• Duration
• Total count of hitches
• Total duration of hitches
• Hitch time ratio
• Frame rate
• Frame count

Emit an os_signpost interval

• Non-animation interval
  • Custom os_signpost with .begin
• Animation interval
  • Custom os_signpost with .animationBegin
  • UIKit instrumented animation interval

/*
 Create an animation os_signpost interval
 Use `.animationBegin`
*/
os_signpost(.animationBegin, log: logHandle, name: "performAnimationInterval")
os_signpost(.end, log: logHandle, name: "performAnimationInterval")

/*
Use a UIKit instrumented animation os_signpost interval
*/
extension XCTOSSignpostMetric {
     open class var navigationTransitionMetric: XCTMetric { get }
     open class var customNavigationTransitionMetric: XCTMetric { get }
     open class var scrollDecelerationMetric: XCTMetric { get }
     open class var scrollDraggingMetric: XCTMetric { get }
}

// TEST

// Measure scrolling animation performance using a Performance XCTest
func testScrollingAnimationPerformance() throws {
    app.launch()
    app.staticTexts["Meal Planner"].tap()
    let foodCollection = app.collectionViews.firstMatch

    let measureOptions = XCTMeasureOptions()
    measureOptions.invocationOptions = [.manuallyStop]

    measure(metrics: [XCTOSSignpostMetric.scrollDecelerationMetric],
            options: measureOptions) {
        foodCollection.swipeUp(velocity: .fast)
        stopMeasuring()
        foodCollection.swipeDown(velocity: .fast)
    }
}

Before Test, change some settings:

• Select performance test target
• Select Release build configuration
• Disable Debugger
• Disable Automatic Screenshots
• Disable Code CoveragexXXX$
• Turn off all diagnostic options under Runtime Sanitization, Runtime API Checking, Memory Management

Test screenshot:

Disk write diagnostics

Created when an app performs more than 1 GB of logical writes within 24hrs

Reference

• https://developer.apple.com/wwdc20/10076
• https://developer.apple.com/documentation/xctest/xctmetric
• https://developer.apple.com/documentation/xctest/xctossignpostmetric