svn commit: r334804 - in head/sys: kern modules/tcp modules/tcp/rack netinet netinet/tcp_stacks sys

[hiren panchasara]

On 06/07/18 at 06:18P, Randall Stewart wrote:
> Author: rrs
> Date: Thu Jun  7 18:18:13 2018
> New Revision: 334804
> URL: https://svnweb.freebsd.org/changeset/base/334804
> 
> Log:
>   This commit brings in a new refactored TCP stack called Rack.
>   Rack includes the following features:
>    - A different SACK processing scheme (the old sack structures are not used).
>    - RACK (Recent acknowledgment) where counting dup-acks is no longer done
>           instead time is used to knwo when to retransmit. (see the I-D)
>    - TLP (Tail Loss Probe) where we will probe for tail-losses to attempt
>           to try not to take a retransmit time-out. (see the I-D)
>    - Burst mitigation using TCPHTPS
>    - PRR (partial rate reduction) see the RFC.
>   
>   Once built into your kernel, you can select this stack by either
>   socket option with the name of the stack is "rack" or by setting
>   the global sysctl so the default is rack.
>   
>   Note that any connection that does not support SACK will be kicked
>   back to the "default" base  FreeBSD stack (currently known as "default").
>   
>   To build this into your kernel you will need to enable in your
>   kernel:
>      makeoptions WITH_EXTRA_TCP_STACKS=1
>      options TCPHPTS
>   
>   Sponsored by:	Netflix Inc.
>   Differential Revision:		https://reviews.freebsd.org/D15525
> 
> Added:
>   head/sys/modules/tcp/rack/
>   head/sys/modules/tcp/rack/Makefile   (contents, props changed)
>   head/sys/netinet/tcp_stacks/rack.c   (contents, props changed)
>   head/sys/netinet/tcp_stacks/rack_bbr_common.h   (contents, props changed)
>   head/sys/netinet/tcp_stacks/sack_filter.c   (contents, props changed)
>   head/sys/netinet/tcp_stacks/sack_filter.h   (contents, props changed)
>   head/sys/netinet/tcp_stacks/tcp_rack.h   (contents, props changed)
> Modified:
>   head/sys/kern/uipc_sockbuf.c
>   head/sys/modules/tcp/Makefile
>   head/sys/netinet/tcp.h
>   head/sys/netinet/tcp_log_buf.h
>   head/sys/netinet/tcp_output.c
>   head/sys/netinet/tcp_stacks/fastpath.c
>   head/sys/netinet/tcp_timer.c
>   head/sys/netinet/tcp_timer.h
>   head/sys/netinet/tcp_var.h
>   head/sys/sys/mbuf.h
>   head/sys/sys/queue.h
>   head/sys/sys/sockbuf.h
>   head/sys/sys/time.h

I thought we'd have more time to review/test this. Looks like BSDCan
commit-spree in effect. :-)

A few questions:
1) Does RACK work reliably without HPTS? If yes, has that config been
tested?

2) It looks like PRR is tied to RACK. Why did we go that route?
Shouldn't it be easily used with the 'default' stack also?

3) Can new SACK be used with the traditional stack?

4) Where should manpage like info for RACK go? a new man-page or
extending tcp(4)? Info like how to enable system-wide or per socket
should go here.

5) Any perf numbers to go along with this commit? Synthetic or
production numbers showing improvements in transfer speed or any other
impact on CPU usage (specially with HPTS) that you can share?

6) In your testing, have you found cases where RACK does poorly compared
to the 'default' stack? Any recommendations on when should RACK be
enabled? (Something like this could go in the manpage.)

Glad to finally see this in -head!

Cheers,
Hiren
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