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Re: Updates to Navigation Timing errata

From: James Simonsen <simonjam@google.com>
Date: Tue, 14 May 2013 10:13:09 -0700
Message-ID: <CAPVJQim8k8AZuPTHkCrpC9pRVc9BTt4W5HxnFDEYxkwjJRWUGA@mail.gmail.com>
To: Boris Zbarsky <bzbarsky@mit.edu>
Cc: public-web-perf <public-web-perf@w3.org>
On Tue, May 14, 2013 at 9:51 AM, Boris Zbarsky <bzbarsky@mit.edu> wrote:

> On 5/14/13 10:49 AM, Philippe Le Hegaret wrote:
>
>> It includes two errata, one regarding the navgiationStart attribute, and
>> one regarding the illustration in 5.1 Processing Model.
>>
>
> I hate sounding like a broken record, but this is still assuming a model
> in which "TCP" comes after "DNS" and "DNS" comes after "Prompt for Unload".
>
> In actual browsers, "DNS" can happen when the user hovers over the link
> that they will click to leave the page (before "Prompt for unload") and
> "TCP" can start before "DNS" completes due to speculative preconnects....
>
> As a result, a browser implementing this specification right now has the
> choice of either not following the spec or reporting numbers that don't
> reflect what it actually did.  In practice I believe at least Gecko ends up
> doing a mix of the two depending on where people remembered to put in
> random max() or min() calls; I can't speak to other browsers.


That's the way it's intended to work. It shows how long each phase is on
the critical path, not necessarily how long it actually took.

FWIW, we do the same thing with min/max.

James
Received on Tuesday, 14 May 2013 17:13:36 UTC

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