Re: [Editorial Errata Reported] RFC7540 (4871)

Mark Nottingham <mnot@mnot.net> Fri, 09 December 2016 03:16 UTC

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From: Mark Nottingham <mnot@mnot.net>
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Date: Fri, 9 Dec 2016 14:12:42 +1100
Cc: Cory Benfield <cory@lukasa.co.uk>, Kazuho Oku <kazuhooku@gmail.com>, Mike Belshe <mike@belshe.com>, Roberto Peon <fenix@google.com>, Alexey Melnikov <aamelnikov@fastmail.fm>, Patrick McManus <pmcmanus@mozilla.com>, HTTP Working Group <ietf-http-wg@w3.org>
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References: <20161130043354.C786DB81319@rfc-editor.org> <1102C272-E8D6-40D3-9D39-7D4801ABD286@lukasa.co.uk> <CABkgnnXYTi0uv=Dm7zPrA=oPam+Zyka-jujFT2bU8GvqvT5JPg@mail.gmail.com> <03C57CE4-E61A-4BF6-A976-2191EB4B127C@lukasa.co.uk> <CANatvzzQZ_isxmd3Ne41QxE2s-sYsrksME+T0RtchM-K1b0DwA@mail.gmail.com> <24141783-A04A-42AD-9730-EB5C91A36516@lukasa.co.uk> <CABkgnnXXLUfC9q5YSQjRWZOqyPevkVrPT2VKvUAEK7caxQDDng@mail.gmail.com>
To: Martin Thomson <martin.thomson@gmail.com>
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Subject: Re: [Editorial Errata Reported] RFC7540 (4871)
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Conversation seems to have concluded - this one is REJECT, correct?

Cheers,


> On 1 Dec. 2016, at 10:03 am, Martin Thomson <martin.thomson@gmail.com> wrote:
> 
> On 1 December 2016 at 00:05, Cory Benfield <cory@lukasa.co.uk> wrote:
>> My understanding of what Martin is suggesting is that that isn’t true:
>> blocked streams do not distribute their weight to their dependants. However,
>> that’s also what the Python Priority implementation does.
> 
> And this was my error in writing up the errata and my earlier emails.
> The spec is clear that there is no functional distinction between
> blocked and finished.  The original text is correct.
> 
> It's pretty obvious however that it's not clear.  I'd answered on the
> basis of first principles, and that was an error on my part.
> 
> Mike's algorithm is almost correct, but I would revise it.  Starting
> at the top level:
> 
> Given a set of dependents of S,
>  find all S where not TreeBlocked(S) as S'
>  allocate resources to S' proportional to their weights
>    for a stream s in S', if StreamBlocked(s), repeat algorithm with
> its dependents
> 
> Not treating closed as special keeps this simple.  If you were to
> treat closed as different to blocked, then you have the issues that
> Cory was digging into.
> 
> Kazuho points out:
>> I also do not see why it would be beneficial to treat them [closed streams] differently.
> 
> It's beneficial if you have other streams that are not blocked that
> don't have dependencies.
> 
> Imagine that you have two HTML files and then images for each as
> dependents.  If one HTML file is blocked, then there is potentially
> less value in loading the images that depend on it than there is in
> making progress on the other HTML file.  Now, that is arguably not
> valuable because HTML/image dependencies are sort of loose, but if you
> have an application that has absolute dependencies (I can't use this
> until you give me that) and other constraints (not enough memory to
> buffer), then you can see a way to treating closed and blocked
> differently.
> 
> Of course, that isn't what the spec says and we don't get to change that :)
> 
> BTW, in answer to what people suggested about flow control, that is
> only one reason a resource might be blocked.  A resource might be
> blocked because the server hasn't finished building it, that might be
> IO or processing.
> 

--
Mark Nottingham   https://www.mnot.net/