Re: [v8-users] performance.now resolution

[Brian Hicks]

Thanks Jakob1

I found out after I sent the original message that performance.now is 
constrained to 5µs resolution anyway for security reasons, but it's good to 
know about the implementation.

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Re: [v8-users] performance.now resolution

[Jakob Kummerow]

Some sort of rounding error, yes. The internal representation (before
converting the value to float) is microseconds. Actual precision depends on
the operating system, as the comment in time.h says:

  // Returns a platform-dependent high-resolution tick count. Implementation
>   // is hardware dependent and may or may not return sub-millisecond
>   // resolution.  THIS CALL IS GENERALLY MUCH MORE EXPENSIVE THAN Now() AND
>   // SHOULD ONLY BE USED WHEN IT IS REALLY NEEDED.


Also, note that V8 itself doesn't know about "performance.now()". It is up
to embedders to provide this functionality -- Chromium has an
implementation, d8 has its own (which is what I'm talking about above), I
don't know about node.js.

On Wed, Feb 1, 2017 at 10:08 AM, Brian Hicks  wrote:

> The spec for performance.now says that the resulting values should be
> accurate to the thousandth of a millisecond. In my testing, I'm getting
> values even more precise than that, down to the ten trillionth place (13
> digits past the decimal)
>
> So my question: is it safe to rely on the values beyond the thousandth
> place, or is this some sort of rounding error or measurement noise?
>
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