Re: Proposal - Reduce HTTP2 frame length from 16 to 12 bits

David Morris <dwm@xpasc.com> Tue, 28 May 2013 21:16 UTC

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Date: Tue, 28 May 2013 14:14:40 -0700 (PDT)
From: David Morris <dwm@xpasc.com>
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Subject: Re: Proposal - Reduce HTTP2 frame length from 16 to 12 bits
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On Tue, 28 May 2013, Patrick McManus wrote:

> On Tue, May 28, 2013 at 4:12 PM, Roberto Peon <grmocg@gmail.com> wrote:
> 
> My sweet-spot number was 16k, as I knew that I could saturate a 10G nic
> > with 16k frames/writes and have enough CPU left over to do some actual
> > work. The amount of overhead goes up more than linearly with the decrease
> > in frame size thanks to contention, etc.
> >
> >
> 
> Given what you've said here and in the other mail (plus of course my own
> previously stated concerns) I'm inclined to suggest a 16KB max (14 bits)
> without introducing any kind of max frame size configurable. My point is to
> drive it as small as we can without creating excessive overhead and you've
> put a stake in the ground that 16KB is that level. That's still 4x as
> aggressive as the current draft.

I've been working with a product for a number of years which incorporates
muxed http response streams where 16k chunks per streams seem to work
well. Our design concern was to keep low speed connections full while
minimizing HOL blocking. Unfortunately, there is no easy way to test
alternatives.