netdev - Re: de-indirect TCP congestion control

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Date:   Mon, 12 Mar 2018 12:48:13 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     David Miller <davem@...emloft.net>
Cc:     eric.dumazet@...il.com, netdev@...r.kernel.org
Subject: Re: de-indirect TCP congestion control

On Mon, 12 Mar 2018 15:04:06 -0400 (EDT)
David Miller <davem@...emloft.net> wrote:

> From: Stephen Hemminger <stephen@...workplumber.org>
> Date: Mon, 12 Mar 2018 11:45:52 -0700
> 
> > Since indirect calls are expensive, and now even more so, perhaps we should figure out
> > a way to make the default TCP congestion control hooks into direct calls.
> > 99% of the users just use the single CC module compiled into the kernel.  
> 
> Who is this magic user with only one CC algorithm enabled in their
> kernel?  I want to know who this dude is?
> 
> I don't think it's going to help much since people will have I think
> at least two algorithms compiled into nearly everyone's tree.
> 
> Distributions will enable everything.
> 
> Google is going to have at least two algorithms enabled.
> 
> etc. etc. etc.
> 
> Getting rid of indirect calls is a fine goal, but the precondition you
> are mentioning to achieve this doesn't seem practical at all.

What I meant is that kernels with N congestion controls, almost all traffic
uses the default So that path can be optimized. The example I gave would
have all the others doing the same indirect call.