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Neal Cardwell a87c83d5ee tcp_bbr: adjust TCP BBR for departure time pacing 
Adjust TCP BBR for the new departure time pacing model in the recent
commit ab408b6dc7 ("tcp: switch tcp and sch_fq to new earliest
departure time model").

With TSQ and pacing at lower layers, there are often several skbs
queued in the pacing layer, and thus there is less data "in the
network" than "in flight".

With departure time pacing at lower layers (e.g. fq or potential
future NICs), the data in the pacing layer now has a pre-scheduled
("baked-in") departure time that cannot be changed, even if the
congestion control algorithm decides to use a new pacing rate.

This means that there can be a non-trivial lag between when BBR makes
a pacing rate change and when the inter-skb pacing delays
change. After a pacing rate change, the number of packets in the
network can gradually evolve to be higher or lower, depending on
whether the sending rate is higher or lower than the delivery
rate. Thus ignoring this lag can cause significant overshoot, with the
flow ending up with too many or too few packets in the network.

This commit changes BBR to adapt its pacing rate based on the amount
of data in the network that it estimates has already been "baked in"
by previous departure time decisions. We estimate the number of our
packets that will be in the network at the earliest departure time
(EDT) for the next skb scheduled as:

   in_network_at_edt = inflight_at_edt - (EDT - now) * bw

If we're increasing the amount of data in the network ("in_network"),
then we want to know if the transmit of the EDT skb will push
in_network above the target, so our answer includes
bbr_tso_segs_goal() from the skb departing at EDT. If we're decreasing
in_network, then we want to know if in_network will sink too low just
before the EDT transmit, so our answer does not include the segments
from the skb departing at EDT.

Why do we treat pacing_gain > 1.0 case and pacing_gain < 1.0 case
differently? The in_network curve is a step function: in_network goes
up on transmits, and down on ACKs. To accurately predict when
in_network will go beyond our target value, this will happen on
different events, depending on whether we're concerned about
in_network potentially going too high or too low:

 o if pushing in_network up (pacing_gain > 1.0),
   then in_network goes above target upon a transmit event

 o if pushing in_network down (pacing_gain < 1.0),
   then in_network goes below target upon an ACK event

This commit changes the BBR state machine to use this estimated
"packets in network" value to make its decisions.

Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
 		2018-10-17 22:22:53 -07:00
Documentation FDDI: defza: Add support for DEC FDDIcontroller 700 TURBOchannel adapter 2018-10-15 21:46:06 -07:00
LICENSES LICENSES: Add Linux-OpenIB license text 2018-04-27 16:41:53 -06:00
arch Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-10-12 21:38:46 -07:00
block blk-mq: I/O and timer unplugs are inverted in blktrace 2018-09-27 13:12:44 -06:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto DMAengine updates for v4.19-rc1 2018-08-18 15:55:59 -07:00
drivers net: phy: mscc: fix memory leak in vsc8574_config_pre_init 2018-10-17 22:08:55 -07:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-10-12 21:38:46 -07:00
include bridge: switchdev: Allow clearing FDB entry offload indication 2018-10-17 17:45:08 -07:00
init Kbuild updates for v4.19 (2nd) 2018-08-25 13:40:38 -07:00
ipc ipc/shm.c: use ERR_CAST() for shm_lock() error return 2018-10-05 16:32:04 -07:00
kernel Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2018-10-15 23:21:07 -07:00
lib Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-10-12 21:38:46 -07:00
mm Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-10-11 12:27:47 +02:00
net tcp_bbr: adjust TCP BBR for departure time pacing 2018-10-17 22:22:53 -07:00
samples Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-10-12 21:38:46 -07:00
scripts Kbuild fixes for v4.19 (2nd) 2018-10-11 19:23:07 +02:00
security Revert "uapi/linux/keyctl.h: don't use C++ reserved keyword as a struct member name" 2018-09-25 13:28:58 +02:00
sound ALSA: hda/realtek - Cannot adjust speaker's volume on Dell XPS 27 7760 2018-10-04 07:50:48 +02:00
tools Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2018-10-15 23:21:07 -07:00
usr initramfs: move gen_initramfs_list.sh from scripts/ to usr/ 2018-08-22 23:21:44 +09:00
virt KVM: Remove obsolete kvm_unmap_hva notifier backend 2018-09-07 15:06:02 +02:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore
…
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2018-10-15 23:21:07 -07:00
Makefile Kbuild fixes for v4.19 (2nd) 2018-10-11 19:23:07 +02:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.