[Webkit-unassigned] [Bug 258572] New: performance.timeOrigin drifts slowly during the lifetime of a page

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=258572

            Bug ID: 258572
           Summary: performance.timeOrigin drifts slowly during the
                    lifetime of a page
           Product: WebKit
           Version: Safari 16
          Hardware: Mac (Apple Silicon)
                OS: macOS 12
            Status: NEW
          Severity: Major
          Priority: P2
         Component: Platform
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: nic at nicj.net

Accessing performance.timeOrigin repeatedly during the lifetime of a page shows that it drifts slowly.

For example, when I first load a page and query performance.timeOrigin I get:

> [new Date, performance.timeOrigin]
< [Tue Jun 27 2023 07:34:57 GMT-0700 (Pacific Daylight Time), 1687876483498.0002]

Then, a few minutes later when I'm querying the same API, I get:

> [new Date, performance.timeOrigin]
< [Tue Jun 27 2023 07:35:37 GMT-0700 (Pacific Daylight Time), 1687876483497]

In this case, it went "backwards" by 1.0002 ms.

Then again a minute later:

> [new Date, performance.timeOrigin]
< [Tue Jun 27 2023 07:36:56 GMT-0700 (Pacific Daylight Time), 1687876483494]

In this case, it went "backwards" by 3ms.

In other instances, I've seen the time drift "forward" slowly over time[1].

timeOrigin should not be changing during the lifetime of the page.

[1] https://docs.google.com/presentation/d/1RW_fLZwUevn7IBXE3hFvKMnaEBs83Dxp3_yLflEfAXk/edit#slide=id.g22706244ab9_0_111

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