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Re: Large Frame Proposal

From: Michael Sweet <msweet@apple.com>
Date: Tue, 08 Jul 2014 08:15:52 -0400
Cc: Greg Wilkins <gregw@intalio.com>, HTTP Working Group <ietf-http-wg@w3.org>
Message-id: <6051FE21-1B31-43F0-BE63-BE46D8DCA3E1@apple.com>
To: Mark Nottingham <mnot@mnot.net>

On Jul 8, 2014, at 12:10 AM, Mark Nottingham <mnot@mnot.net> wrote:
> Michael,
> On 8 Jul 2014, at 12:06 pm, Michael Sweet <msweet@apple.com> wrote:
>> Mark,
>> On Jul 7, 2014, at 8:58 PM, Mark Nottingham <mnot@mnot.net> wrote:
>>>> ...
>>>> Or at least one issue that the fixed max frame size cannot be tuned for any reason
>>> That's a design decision that was made a long time ago. To reconsider it, I need more than vague concerns that amount to "I don't like it"; I need concrete problems that it causes.
>> For printing 16k frames/chunks cause a 2x performance drop.  And for video streaming you'll likely see similar issues (and stuttering) due to the volume of data involved. (see my other post on the subject)
> Out of curiosity - are your use cases *actually* using HTTP/2, or are you assuming some mapping of IPP to HTTP/2?

I'm applying our experience with HTTP/1.1 chunk sizes to HTTP/2; as I mentioned in my original (more detailed) response yesterday, there are no HTTP/2-based IPP printers (yet), but that is one of the projects I am working on right now... Since IPP is just another POST-based RPC scheme (using the IPP binary message encoding vs. XML or JSON) the only real change here is to using HTTP/2 in place of HTTP/1.1 as the transport.

The original message was in response to claims that smaller frame sizes will not adversely affect performance, but I provided experience with running code that we saw issues in HTTP/1.1 with smaller chunks and that a modest increase in chunk size provided  a dramatic performance improvement for all printers.  There is no reason to expect any different experience in HTTP/2, as the HTTP/2 frame overhead (8 bytes currently) is generally the same as the HTTP/1.1 chunking overhead ("3fff\r\n" + "\r\n" = 8 bytes)  with similar CPU processing requirements.

Michael Sweet, Senior Printing System Engineer, PWG Chair

Received on Tuesday, 8 July 2014 12:16:24 UTC

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