Re: de-indirect TCP congestion control

On Mon, 12 Mar 2018 16:05:16 -0400 (EDT)
David Miller [off-list ref] wrote:

From: Eric Dumazet <redacted>
Date: Mon, 12 Mar 2018 13:03:35 -0700

quoted

On 03/12/2018 12:48 PM, Stephen Hemminger wrote:  

quoted

On Mon, 12 Mar 2018 15:04:06 -0400 (EDT)
David Miller [off-list ref] wrote:
  

quoted

From: Stephen Hemminger <stephen@networkplumber.org>
Date: Mon, 12 Mar 2018 11:45:52 -0700
 

quoted

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.  

I do not understand. What is default_tcp_ops anyway ?

How changes to /proc/sys/net/ipv4/tcp_congestion_control will impact
this ?  

I'm also confused what is being suggested exactly and how this can
work. :-)

Trying to directly call the fastpath TCP congestion operations for sockets
using the default.  The problem is how to do this and it gets messy with Kconfig
and CPP to deal with as raw tools. Maybe weak symbols could be used.