ECN (ABE)" proposal to the New Reno congestion control algorithm module.
ABE reduces the amount of congestion window reduction in response to
ECN-signalled congestion relative to the loss-inferred congestion response.
More details about ABE can be found in the Internet-Draft:
https://tools.ietf.org/html/draft-ietf-tcpm-alternativebackoff-ecn
The implementation introduces four new sysctls:
- net.inet.tcp.cc.abe defaults to 0 (disabled) and can be set to non-zero to
enable ABE for ECN-enabled TCP connections.
- net.inet.tcp.cc.newreno.beta and net.inet.tcp.cc.newreno.beta_ecn set the
multiplicative window decrease factor, specified as a percentage, applied to
the congestion window in response to a loss-based or ECN-based congestion
signal respectively. They default to the values specified in the draft i.e.
beta=50 and beta_ecn=80.
- net.inet.tcp.cc.abe_frlossreduce defaults to 0 (disabled) and can be set to
non-zero to enable the use of standard beta (50% by default) when repairing
loss during an ECN-signalled congestion recovery episode. It enables a more
conservative congestion response and is provided for the purposes of
experimentation as a result of some discussion at IETF 100 in Singapore.
The values of beta and beta_ecn can also be set per-connection by way of the
TCP_CCALGOOPT TCP-level socket option and the new CC_NEWRENO_BETA or
CC_NEWRENO_BETA_ECN CC algo sub-options.
Submitted by: Tom Jones <tj@enoti.me>
Tested by: Tom Jones <tj@enoti.me>, Grenville Armitage <garmitage@swin.edu.au>
Relnotes: Yes
Differential Revision: https://reviews.freebsd.org/D11616
Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.
The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.
No functional change intended.
directly accessed. Although this will work on some platforms, it can
throw an exception if the pointer is invalid and then panic the kernel.
Add a missing SYSCTL_IN() of "SCTP_BASE_STATS" structure.
MFC after: 3 days
Sponsored by: Mellanox Technologies
write to the buffer causes it to overflow. We therefore can't hold the CC list
rwlock over a call to sbuf_printf() for an sbuf configured with SBUF_AUTOEXTEND.
Switch to a fixed length sbuf which should be of sufficient size except in the
very unlikely event that the sysctl is being processed as one or more new
algorithms are loaded. If that happens, we accept the race and may fail the
sysctl gracefully if there is insufficient room to print the names of all the
algorithms.
This should address a WITNESS warning and the potential panic that would occur
if the sbuf call to malloc did sleep whilst holding the CC list rwlock.
Sponsored by: FreeBSD Foundation
Reported by: Nick Hibma
Reviewed by: bz
MFC after: 3 weeks
X-MFC with: r215166
vnets to select their own default CC algorithm independent of each other and the
base system. If the base system or a vnet has set a default which gets unloaded,
we reset that netstack's default to NewReno.
Sponsored by: FreeBSD Foundation
Tested by: Mikolaj Golub <to.my.trociny at gmail com>
Reviewed by: bz (briefly)
MFC after: 3 months
is small, so there is no good reason not to declare the buffer at the top.
- Fix a whitespace nit.
Sponsored by: FreeBSD Foundation
MFC after: 11 weeks
X-MFC with: r215166
Any found to be using the algorithm that is about to go away are switched back
to NewReno to avoid leaving dangling pointers which would trigger a panic. For
VIMAGE kernels, there is a list per vnet to walk, yet the implementation was
only examining one of the vnet lists.
Fix the implementation of the above feature for VIMAGE kernels by looping
through all active TCP control blocks across all vnets.
Sponsored by: FreeBSD Foundation
Tested by: Mikolaj Golub <to.my.trociny at gmail com>
Reviewed by: bz (briefly)
MFC after: 11 weeks
runs on boot and each time a vnet jail is created. Running cc_init() multiple
times results in a panic when attempting to initialise the cc_list lock again,
and so r215166 effectively broke the use of vnet jails.
Switch to using a SYSINIT to run cc_init() on boot. CC algorithm modules loaded
on boot register in the same SI_SUB_PROTO_IFATTACHDOMAIN category as is used in
this patch, so cc_init() is run at SI_ORDER_FIRST to ensure the framework is
initialised before module registration is attempted.
Sponsored by: FreeBSD Foundation
Reported and tested by: Mikolaj Golub <to.my.trociny at gmail com>
MFC after: 11 weeks
X-MFC with: r215166
Control Algorithms for FreeBSD" FreeBSD Foundation funded project. More details
about the project are available at: http://caia.swin.edu.au/freebsd/5cc/
- Add a KPI and supporting infrastructure to allow modular congestion control
algorithms to be used in the net stack. Algorithms can maintain per-connection
state if required, and connections maintain their own algorithm pointer, which
allows different connections to concurrently use different algorithms. The
TCP_CONGESTION socket option can be used with getsockopt()/setsockopt() to
programmatically query or change the congestion control algorithm respectively
from within an application at runtime.
- Integrate the framework with the TCP stack in as least intrusive a manner as
possible. Care was also taken to develop the framework in a way that should
allow integration with other congestion aware transport protocols (e.g. SCTP)
in the future. The hope is that we will one day be able to share a single set
of congestion control algorithm modules between all congestion aware transport
protocols.
- Introduce a new congestion recovery (TF_CONGRECOVERY) state into the TCP stack
and use it to decouple the meaning of recovery from a congestion event and
recovery from packet loss (TF_FASTRECOVERY) a la RFC2581. ECN and delay based
congestion control protocols don't generally need to recover from packet loss
and need a different way to note a congestion recovery episode within the
stack.
- Remove the net.inet.tcp.newreno sysctl, which simplifies some portions of code
and ensures the stack always uses the appropriate mechanisms for recovering
from packet loss during a congestion recovery episode.
- Extract the NewReno congestion control algorithm from the TCP stack and
massage it into module form. NewReno is always built into the kernel and will
remain the default algorithm for the forseeable future. Implementations of
additional different algorithms will become available in the near future.
- Bump __FreeBSD_version to 900025 and note in UPDATING that rebuilding code
that relies on the size of "struct tcpcb" is required.
Many thanks go to the Cisco University Research Program Fund at Community
Foundation Silicon Valley and the FreeBSD Foundation. Their support of our work
at the Centre for Advanced Internet Architectures, Swinburne University of
Technology is greatly appreciated.
In collaboration with: David Hayes <dahayes at swin edu au> and
Grenville Armitage <garmitage at swin edu au>
Sponsored by: Cisco URP, FreeBSD Foundation
Reviewed by: rpaulo
Tested by: David Hayes (and many others over the years)
MFC after: 3 months
