Subject: [PATCH net-next 0/3] Implementation of RFC 4898 Extended TCP Statistics (Web10G)

From: rapier <[email-masked]>
Date: Tue, 16 Dec 2014 12:49:59 -0500

The following patch increments and/or update select RFC 4898 (TCP 
Extended Statistics MIB) metrics within the TCP stack; we refer to this 
as the Kernel Instrument Set (or KIS).  The goal of RFC 4898 is to 
expose advanced statistics from TCP’s vantage point to userland in order 
to help diagnose performance problems in both the network and 
application. The metrics are gathered and cached within structures 
defined in our header file (tcp_estats.h) on a per connection basis 
allowing for highly detailed analysis of all TCP flows. More information 
can be found at http://www.web10g.org/

Note, the KIS does not integrate any specific ABI. This allows for a
clear separation between the kernel instruments and the methodology used
to make the metrics available to userland. Currently, we have a netlink
implementation available as a DLKM and an associated API available at
https://sourceforge.net/projects/tcpestats/files/

Performance analysis provided by the kernel development teams at Google
and Facebook indicate that the overhead imposed when the KIS is
configured active and exposed via an ABI are minimal.  Facebook related
performance impacts of between 0% and 2%, depending on the the frequency
of polling the KIS via ftrace.  Analysis performed at Google indicate
similar performance characteristics.

Since the size of the KIS patch set is considerable (~2k lines), we have
broken it up into two components, the first provides our structures and 
macros to the TCP networking DLKMs. The second provides the routines 
that manage and control the TCP Extended Statistics, as well as 
providing hooks for configuring and enabling the KIS. Each set of 
patches patches, compiles, and runs independently. However, full 
functionality requires both patch sets to be installed.

We took this approach because the control and management (C&M) routines 
are, in our view, of secondary importance to the actual instrumentation. 
As such, we did not want any issues with the C&M methods to impact the 
adoption of the KIS. There is overlap between the two patch sets 
(specifically the header files in the C&M) which will likely make 
applying the C&M patch cleanly on top of the KIS patch problematic. As 
such, I've also included a concatenated patch that includes both the KIS 
and the C&M for evaluation.

A git repo is available at http://github.com/rapier/web10g The
net-next branch contains the instrumentation (1st patch set) and the
control and management (2nd patch set). The API is also available at
http://github.com/rapier1/web10g-userland

Chris Rapier