Add support of an offset value for incremental counter and random. With
this option the sysadmin is able to start the counter to a certain value
and then apply the generated number.
Example:
meta mark set numgen inc mod 2 offset 100
This will generate marks with the serie 100, 101, 100, 101, ...
Suggested-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Laura Garcia Liebana <nevola@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
stop_two_cpus() and stop_cpus() use stop_cpus_lock to avoid the deadlock,
we need to ensure that the stopper functions can't be queued "backwards"
from one another. This doesn't look nice; if we use lglock then we do not
really need stopper->lock, cpu_stop_queue_work() could use lg_local_lock()
under local_irq_save().
OTOH it would be even better to avoid lglock in stop_machine.c and remove
lg_double_lock(). This patch adds "bool stop_cpus_in_progress" set/cleared
by queue_stop_cpus_work(), and changes cpu_stop_queue_two_works() to busy
wait until it is cleared.
queue_stop_cpus_work() sets stop_cpus_in_progress = T lockless, but after
it queues a work on CPU1 it must be visible to stop_two_cpus(CPU1, CPU2)
which checks it under the same lock. And since stop_two_cpus() holds the
2nd lock too, queue_stop_cpus_work() can not clear stop_cpus_in_progress
if it is also going to queue a work on CPU2, it needs to take that 2nd
lock to do this.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20151121181148.GA433@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Provide a down_read()/up_read() variant that keeps preemption disabled
over the whole thing, when possible.
This avoids a needless preemption point for constructs such as:
percpu_down_read(&global_rwsem);
spin_lock(&lock);
...
spin_unlock(&lock);
percpu_up_read(&global_rwsem);
Which perturbs timings. In particular it was found to cure a
performance regression in a follow up patch in fs/locks.c
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
As warned by linuxdoc[1] tool, using:
$ for i in $(git grep kernel-doc Documentation/media/kapi/|cut -d: -f4); do kernel-lintdoc --sloppy $i; done
include/media/v4l2-dev.h:118 :WARN: function name from comment differs: v4l2_prio_close <--> v4l2_prio_check
include/media/v4l2-mc.h:56 [kernel-doc WARN] : enum name from comment differs: if_vid_dec_index <--> if_vid_dec_pad_index
include/media/v4l2-mc.h:71 [kernel-doc WARN] : enum name from comment differs: if_aud_dec_index <--> if_aud_dec_pad_index
include/media/v4l2-mem2mem.h:396 [kernel-doc WARN] : function name from comment differs: v4l2_m2m_num_src_bufs_ready <--> v4l2_m2m_num_dst_bufs_ready
drivers/media/dvb-core/dvb_math.h:28 [kernel-doc WARN] : function name from comment differs: cintlog2 <--> intlog2
include/media/v4l2-subdev.h:215 [kernel-doc WARN] : struct name from comment differs: s_radio <--> v4l2_subdev_tuner_ops
include/media/v4l2-subdev.h:890 [kernel-doc WARN] : function name from comment differs: v4l2_set_subdevdata <--> v4l2_set_subdev_hostdata
include/media/v4l2-subdev.h:901 [kernel-doc WARN] : function name from comment differs: v4l2_get_subdevdata <--> v4l2_get_subdev_hostdata
drivers/media/dvb-core/dvb_ringbuffer.h:196 [kernel-doc WARN] : function name from comment differs: dvb_ringbuffer_writeuser <--> dvb_ringbuffer_write_user
include/media/videobuf2-core.h:399 [kernel-doc WARN] : struct name from comment differs: vb2_ops <--> vb2_buf_ops
include/media/media-entity.h:132 [kernel-doc ERROR] : duplicate parameter definition 'source'
include/media/media-entity.h:477 [kernel-doc WARN] : function name from comment differs: media_entity_enum_test <--> media_entity_enum_test_and_set
include/media/media-entity.h:535 [kernel-doc WARN] : function name from comment differs: gobj_to_entity <--> gobj_to_pad
include/media/media-entity.h:544 [kernel-doc WARN] : function name from comment differs: gobj_to_entity <--> gobj_to_link
include/media/media-entity.h:553 [kernel-doc WARN] : function name from comment differs: gobj_to_entity <--> gobj_to_intf
include/media/media-entity.h:562 [kernel-doc WARN] : function name from comment differs: gobj_to_entity <--> intf_to_devnode
include/media/rc-core.h:234 [kernel-doc WARN] : function name from comment differs: rc_open <--> rc_close
include/media/v4l2-ctrls.h:397 [kernel-doc WARN] : missing initial short description of 'v4l2_ctrl_handler_init'
include/media/v4l2-dev.h:118 [kernel-doc WARN] : function name from comment differs: v4l2_prio_close <--> v4l2_prio_check
include/media/v4l2-event.h:225 [kernel-doc WARN] : missing initial short description of 'v4l2_src_change_event_subscribe'
[1] https://return42.github.io/linuxdoc/linux.html
The above are real issues at the documentation. On several cases,
caused by cut-and-paste.
Fix them.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Enabling -ffunction-sections modified the generic linker script to
pull .text.* sections into regular TEXT_TEXT section, conflicting
with some architectures. Revert that change and require archs that
enable the option to ensure they have no conflicting section names,
and do the appropriate merging.
Reported-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Fixes: b67067f117 ("kbuild: allow archs to select link dead code/data elimination")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.com>
adds PHY-mode "trgmii" as an extension for the operation
mode of the PHY interface for PHY_INTERFACE_MODE_TRGMII.
and adds a variable trgmii inside mtk_mac as the indication
to make the difference between the MAC connected to internal
switch or connected to external PHY by the given configuration
on the board and then to perform the corresponding setup on
TRGMII hardware module.
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
David Howells says:
====================
rxrpc: Preparation for slow-start algorithm [ver #2]
Here are some patches that prepare for improvements in ACK generation and
for the implementation of the slow-start part of the protocol:
(1) Stop storing the protocol header in the Tx socket buffers, but rather
generate it on the fly. This potentially saves a little space and
makes it easier to alter the header just before transmission (the
flags may get altered and the serial number has to be changed).
(2) Mask off the Tx buffer annotations and add a flag to record which ones
have already been resent.
(3) Track RTT on a per-peer basis for use in future changes. Tracepoints
are added to log this.
(4) Send PING ACKs in response to incoming calls to elicit a PING-RESPONSE
ACK from which RTT data can be calculated. The response also carries
other useful information.
(5) Expedite PING-RESPONSE ACK generation from sendmsg. If we're actively
using sendmsg, this allows us, under some circumstances, to avoid
having to rely on the background work item to run to generate this
ACK.
This requires ktime_sub_ms() to be added.
(6) Set the REQUEST-ACK flag on some DATA packets to elicit ACK-REQUESTED
ACKs from which RTT data can be calculated.
(7) Limit the use of pings and ACK requests for RTT determination.
Changes:
(V2) Don't use the C division operator for 64-bit division. One instance
should use do_div() and the other should be using nsecs_to_jiffies().
The last two patches got transposed, leading to an undefined symbol
in one of them.
Reported-by: kbuild test robot <lkp@intel.com>
====================
Signed-off-by: David S. Miller <davem@davemloft.net>
This patch allows to build and use vgic-v3 in 32-bit mode.
Unfortunately, it can not be split in several steps without extra
stubs to keep patches independent and bisectable. For instance,
virt/kvm/arm/vgic/vgic-v3.c uses function from vgic-v3-sr.c, handling
access to GICv3 cpu interface from the guest requires vgic_v3.vgic_sre
to be already defined.
It is how support has been done:
* handle SGI requests from the guest
* report configured SRE on access to GICv3 cpu interface from the guest
* required vgic-v3 macros are provided via uapi.h
* static keys are used to select GIC backend
* to make vgic-v3 build KVM_ARM_VGIC_V3 guard is removed along with
the static inlines
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Currently GIC backend is selected via alternative framework and this
is fine. We are going to introduce vgic-v3 to 32-bit world and there
we don't have patching framework in hand, so we can either check
support for GICv3 every time we need to choose which backend to use or
try to optimise it by using static keys. The later looks quite
promising because we can share logic involved in selecting GIC backend
between architectures if both uses static keys.
This patch moves arm64 from alternative to static keys framework for
selecting GIC backend. For that we embed static key into vgic_global
and enable the key during vgic initialisation based on what has
already been exposed by the host GIC driver.
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
inode_change_ok() will be resposible for clearing capabilities and IMA
extended attributes and as such will need dentry. Give it as an argument
to inode_change_ok() instead of an inode. Also rename inode_change_ok()
to setattr_prepare() to better relect that it does also some
modifications in addition to checks.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
When file permissions are modified via chmod(2) and the user is not in
the owning group or capable of CAP_FSETID, the setgid bit is cleared in
inode_change_ok(). Setting a POSIX ACL via setxattr(2) sets the file
permissions as well as the new ACL, but doesn't clear the setgid bit in
a similar way; this allows to bypass the check in chmod(2). Fix that.
References: CVE-2016-7097
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
A timer was used to restart after the bus-off state, leading to a
relatively large can_restart() executed in an interrupt context,
which in turn sets up pinctrl. When this happens during system boot,
there is a high probability of grabbing the pinctrl_list_mutex,
which is locked already by the probe() of other device, making the
kernel suspect a deadlock condition [1].
To resolve this issue, the restart_timer is replaced by a delayed
work.
[1] https://github.com/victronenergy/venus/issues/24
Signed-off-by: Sergei Miroshnichenko <sergeimir@emcraft.com>
Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
To something more meaningful these days, specially because this is
working on packet headers or lengths and which are not tied to any CPU
arch but to the protocol itself.
So, WORD_TRUNC becomes SCTP_TRUNC4 and WORD_ROUND becomes SCTP_PAD4.
Reported-by: David Laight <David.Laight@ACULAB.COM>
Reported-by: David Miller <davem@davemloft.net>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Just pure code movement, cleanup and polish will happen in later
patches.
v2: Don't forget all the ioctl! To extract those cleanly I decided to
put check_src_coords into drm_framebuffer.c (and give it a
drm_framebuffer_ prefix), since that just checks framebuffer
constraints.
v3: rebase over PAGE_FLIP_TARGET.
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
[seanpaul]
This patch as posted on the list was rebased on:
commit 6f00975c61
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date: Sat Aug 20 12:22:11 2016 +0200
drm: Reject page_flip for !DRIVER_MODESET
so as a result of moving the page_flip ioctl, this fix has
been rolled into this patch.
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Steffen Klassert says:
====================
pull request (net): ipsec 2016-09-21
1) Propagate errors on security context allocation.
From Mathias Krause.
2) Fix inbound policy checks for inter address family tunnels.
From Thomas Zeitlhofer.
3) Fix an old memory leak on aead algorithm usage.
From Ilan Tayari.
4) A recent patch fixed a possible NULL pointer dereference
but broke the vti6 input path.
Fix from Nicolas Dichtel.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>
Drivers must be ready to accept NULL from ptp_clock_register() if the
PTP clock subsystem is configured out.
This patch documents that and ensures that all drivers cope well
with a NULL return.
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Reviewed-by: Eugenia Emantayev <eugenia@mellanox.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Acked-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
TCA_VLAN_ACT_MODIFY allows one to change an existing tag.
It accepts same attributes as TCA_VLAN_ACT_PUSH (protocol, id,
priority).
If packet is vlan tagged, then the tag gets overwritten according to
user specified attributes.
For example, this allows user to replace a tag's vid while preserving
its priority bits (as opposed to "action vlan pop pipe action vlan push").
Signed-off-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This exports the functionality of extracting the tag from the payload,
without moving next vlan tag into hw accel tag.
Signed-off-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Add a function to track the average RTT for a peer. Sources of RTT data
will be added in subsequent patches.
The RTT data will be useful in the future for determining resend timeouts
and for handling the slow-start part of the Rx protocol.
Also add a pair of tracepoints, one to log transmissions to elicit a
response for RTT purposes and one to log responses that contribute RTT
data.
Signed-off-by: David Howells <dhowells@redhat.com>
Advanced JIT compilers and translators may want to use
eBPF verifier as a base for parsers or to perform custom
checks and validations.
Add ability for external users to invoke the verifier
and provide callbacks to be invoked for every intruction
checked. For now only add most basic callback for
per-instruction pre-interpretation checks is added. More
advanced users may also like to have per-instruction post
callback and state comparison callback.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Move verifier's internal structures to a header file and
prefix their names with bpf_ to avoid potential namespace
conflicts. Those structures will soon be used by external
analyzers.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Add cls_bpf support for the TCA_CLS_FLAGS_SKIP_HW flag.
Unlike U32 and flower cls_bpf already has some netlink
flags defined. Create a new attribute to be able to use
the same flag values as the above.
Unlike U32 and flower reject unknown flags.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This patch adds hardware offload capability to cls_bpf classifier,
similar to what have been done with U32 and flower.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Optimize RAID6 recovery functions to take advantage of
the 512-bit ZMM integer instructions introduced in AVX512.
AVX512 optimized recovery functions, which is simply based
on recov_avx2.c written by Jim Kukunas
This patch was tested and benchmarked before submission on
a hardware that has AVX512 flags to support such instructions
Cc: Jim Kukunas <james.t.kukunas@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Megha Dey <megha.dey@linux.intel.com>
Signed-off-by: Gayatri Kammela <gayatri.kammela@intel.com>
Reviewed-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Shaohua Li <shli@fb.com>
Optimize RAID6 gen_syndrom functions to take advantage of
the 512-bit ZMM integer instructions introduced in AVX512.
AVX512 optimized gen_syndrom functions, which is simply based
on avx2.c written by Yuanhan Liu and sse2.c written by hpa.
The patch was tested and benchmarked before submission on
a hardware that has AVX512 flags to support such instructions
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jim Kukunas <james.t.kukunas@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Megha Dey <megha.dey@linux.intel.com>
Signed-off-by: Gayatri Kammela <gayatri.kammela@intel.com>
Reviewed-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Shaohua Li <shli@fb.com>
For a host to access an Open-Channel SSD, it has to know its geometry,
so that it writes and reads at the appropriate device bounds.
Currently, the geometry information is kept within the kernel, and not
exported to user-space for consumption. This patch exposes the
configuration through sysfs and enables user-space libraries, such as
liblightnvm, to use the sysfs implementation to get the geometry of an
Open-Channel SSD.
The sysfs entries are stored within the device hierarchy, and can be
found using the "lightnvm" device type.
An example configuration looks like this:
/sys/class/nvme/
└── nvme0n1
├── capabilities: 3
├── device_mode: 1
├── erase_max: 1000000
├── erase_typ: 1000000
├── flash_media_type: 0
├── media_capabilities: 0x00000001
├── media_type: 0
├── multiplane: 0x00010101
├── num_blocks: 1022
├── num_channels: 1
├── num_luns: 4
├── num_pages: 64
├── num_planes: 1
├── page_size: 4096
├── prog_max: 100000
├── prog_typ: 100000
├── read_max: 10000
├── read_typ: 10000
├── sector_oob_size: 0
├── sector_size: 4096
├── media_manager: gennvm
├── ppa_format: 0x380830082808001010102008
├── vendor_opcode: 0
├── max_phys_secs: 64
└── version: 1
Signed-off-by: Simon A. F. Lund <slund@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>
LightNVM compatible device drivers does not have a method to expose
LightNVM specific sysfs entries.
To enable LightNVM sysfs entries to be exposed, lightnvm device
drivers require a struct device to attach it to. To allow both the
actual device driver and lightnvm sysfs entries to coexist, the device
driver tracks the lifetime of the nvm_dev structure.
This patch refactors NVMe and null_blk to handle the lifetime of struct
nvm_dev, which eliminates the need for struct gendisk when a lightnvm
compatible device is provided.
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>
Enable devices without a gendisk instance to register itself with blk-mq
and expose the associated multi-queue sysfs entries.
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>
This patch introduces an accessor which can be used
by the users of debugfs (drivers, fs, ...) to get the
original file_operations struct. It also removes the
REAL_FOPS_DEREF macro in file.c and converts the code
to use the public version.
Previously, REAL_FOPS_DEREF was only available within
the file.c of debugfs. But having a public getter
available for debugfs users is important as some
drivers (carl9170 and b43) use the pointer of the
original file_operations in conjunction with container_of()
within their debugfs implementations.
Reviewed-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Cc: stable <stable@vger.kernel.org> # 4.7+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Since commit 1625f45299, vti6 is broken, all input packets are dropped
(LINUX_MIB_XFRMINNOSTATES is incremented).
XFRM_TUNNEL_SKB_CB(skb)->tunnel.ip6 is set by vti6_rcv() before calling
xfrm6_rcv()/xfrm6_rcv_spi(), thus we cannot set to NULL that value in
xfrm6_rcv_spi().
A new function xfrm6_rcv_tnl() that enables to pass a value to
xfrm6_rcv_spi() is added, so that xfrm6_rcv() is not touched (this function
is used in several handlers).
CC: Alexey Kodanev <alexey.kodanev@oracle.com>
Fixes: 1625f45299 ("net/xfrm_input: fix possible NULL deref of tunnel.ip6->parms.i_key")
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
This commit implements a new TCP congestion control algorithm: BBR
(Bottleneck Bandwidth and RTT). A detailed description of BBR will be
published in ACM Queue, Vol. 14 No. 5, September-October 2016, as
"BBR: Congestion-Based Congestion Control".
BBR has significantly increased throughput and reduced latency for
connections on Google's internal backbone networks and google.com and
YouTube Web servers.
BBR requires only changes on the sender side, not in the network or
the receiver side. Thus it can be incrementally deployed on today's
Internet, or in datacenters.
The Internet has predominantly used loss-based congestion control
(largely Reno or CUBIC) since the 1980s, relying on packet loss as the
signal to slow down. While this worked well for many years, loss-based
congestion control is unfortunately out-dated in today's networks. On
today's Internet, loss-based congestion control causes the infamous
bufferbloat problem, often causing seconds of needless queuing delay,
since it fills the bloated buffers in many last-mile links. On today's
high-speed long-haul links using commodity switches with shallow
buffers, loss-based congestion control has abysmal throughput because
it over-reacts to losses caused by transient traffic bursts.
In 1981 Kleinrock and Gale showed that the optimal operating point for
a network maximizes delivered bandwidth while minimizing delay and
loss, not only for single connections but for the network as a
whole. Finding that optimal operating point has been elusive, since
any single network measurement is ambiguous: network measurements are
the result of both bandwidth and propagation delay, and those two
cannot be measured simultaneously.
While it is impossible to disambiguate any single bandwidth or RTT
measurement, a connection's behavior over time tells a clearer
story. BBR uses a measurement strategy designed to resolve this
ambiguity. It combines these measurements with a robust servo loop
using recent control systems advances to implement a distributed
congestion control algorithm that reacts to actual congestion, not
packet loss or transient queue delay, and is designed to converge with
high probability to a point near the optimal operating point.
In a nutshell, BBR creates an explicit model of the network pipe by
sequentially probing the bottleneck bandwidth and RTT. On the arrival
of each ACK, BBR derives the current delivery rate of the last round
trip, and feeds it through a windowed max-filter to estimate the
bottleneck bandwidth. Conversely it uses a windowed min-filter to
estimate the round trip propagation delay. The max-filtered bandwidth
and min-filtered RTT estimates form BBR's model of the network pipe.
Using its model, BBR sets control parameters to govern sending
behavior. The primary control is the pacing rate: BBR applies a gain
multiplier to transmit faster or slower than the observed bottleneck
bandwidth. The conventional congestion window (cwnd) is now the
secondary control; the cwnd is set to a small multiple of the
estimated BDP (bandwidth-delay product) in order to allow full
utilization and bandwidth probing while bounding the potential amount
of queue at the bottleneck.
When a BBR connection starts, it enters STARTUP mode and applies a
high gain to perform an exponential search to quickly probe the
bottleneck bandwidth (doubling its sending rate each round trip, like
slow start). However, instead of continuing until it fills up the
buffer (i.e. a loss), or until delay or ACK spacing reaches some
threshold (like Hystart), it uses its model of the pipe to estimate
when that pipe is full: it estimates the pipe is full when it notices
the estimated bandwidth has stopped growing. At that point it exits
STARTUP and enters DRAIN mode, where it reduces its pacing rate to
drain the queue it estimates it has created.
Then BBR enters steady state. In steady state, PROBE_BW mode cycles
between first pacing faster to probe for more bandwidth, then pacing
slower to drain any queue that created if no more bandwidth was
available, and then cruising at the estimated bandwidth to utilize the
pipe without creating excess queue. Occasionally, on an as-needed
basis, it sends significantly slower to probe for RTT (PROBE_RTT
mode).
BBR has been fully deployed on Google's wide-area backbone networks
and we're experimenting with BBR on Google.com and YouTube on a global
scale. Replacing CUBIC with BBR has resulted in significant
improvements in network latency and application (RPC, browser, and
video) metrics. For more details please refer to our upcoming ACM
Queue publication.
Example performance results, to illustrate the difference between BBR
and CUBIC:
Resilience to random loss (e.g. from shallow buffers):
Consider a netperf TCP_STREAM test lasting 30 secs on an emulated
path with a 10Gbps bottleneck, 100ms RTT, and 1% packet loss
rate. CUBIC gets 3.27 Mbps, and BBR gets 9150 Mbps (2798x higher).
Low latency with the bloated buffers common in today's last-mile links:
Consider a netperf TCP_STREAM test lasting 120 secs on an emulated
path with a 10Mbps bottleneck, 40ms RTT, and 1000-packet bottleneck
buffer. Both fully utilize the bottleneck bandwidth, but BBR
achieves this with a median RTT 25x lower (43 ms instead of 1.09
secs).
Our long-term goal is to improve the congestion control algorithms
used on the Internet. We are hopeful that BBR can help advance the
efforts toward this goal, and motivate the community to do further
research.
Test results, performance evaluations, feedback, and BBR-related
discussions are very welcome in the public e-mail list for BBR:
https://groups.google.com/forum/#!forum/bbr-dev
NOTE: BBR *must* be used with the fq qdisc ("man tc-fq") with pacing
enabled, since pacing is integral to the BBR design and
implementation. BBR without pacing would not function properly, and
may incur unnecessary high packet loss rates.
Signed-off-by: Van Jacobson <vanj@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Nandita Dukkipati <nanditad@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
