11b9695b3f
9 Commits
| Author | SHA1 | Message | Date | |
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Dave Taht
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2db6dc2662 |
sch_cake: Make gso-splitting configurable from userspace
This patch restores cake's deployed behavior at line rate to always
split gso, and makes gso splitting configurable from userspace.
running cake unlimited (unshaped) at 1gigE, local traffic:
no-split-gso bql limit: 131966
split-gso bql limit: ~42392-45420
On this 4 stream test splitting gso apart results in halving the
observed interpacket latency at no loss in throughput.
Summary of tcp_nup test run 'gso-split' (at 2018-07-26 16:03:51.824728):
Ping (ms) ICMP : 0.83 0.81 ms 341
TCP upload avg : 235.43 235.39 Mbits/s 301
TCP upload sum : 941.71 941.56 Mbits/s 301
TCP upload::1 : 235.45 235.43 Mbits/s 271
TCP upload::2 : 235.45 235.41 Mbits/s 289
TCP upload::3 : 235.40 235.40 Mbits/s 288
TCP upload::4 : 235.41 235.40 Mbits/s 291
verses
Summary of tcp_nup test run 'no-split-gso' (at 2018-07-26 16:37:23.563960):
avg median # data pts
Ping (ms) ICMP : 1.67 1.73 ms 348
TCP upload avg : 234.56 235.37 Mbits/s 301
TCP upload sum : 938.24 941.49 Mbits/s 301
TCP upload::1 : 234.55 235.38 Mbits/s 285
TCP upload::2 : 234.57 235.37 Mbits/s 286
TCP upload::3 : 234.58 235.37 Mbits/s 274
TCP upload::4 : 234.54 235.42 Mbits/s 288
Signed-off-by: David S. Miller <davem@davemloft.net>
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Toke Høiland-Jørgensen
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301f935be9 |
sch_cake: Fix tin order when set through skb->priority
In diffserv mode, CAKE stores tins in a different order internally than
the logical order exposed to userspace. The order remapping was missing
in the handling of 'tc filter' priority mappings through skb->priority,
resulting in bulk and best effort mappings being reversed relative to
how they are displayed.
Fix this by adding the missing mapping when reading skb->priority.
Fixes:
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Toke Høiland-Jørgensen
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0c850344d3 |
sch_cake: Conditionally split GSO segments
At lower bandwidths, the transmission time of a single GSO segment can add an unacceptable amount of latency due to HOL blocking. Furthermore, with a software shaper, any tuning mechanism employed by the kernel to control the maximum size of GSO segments is thrown off by the artificial limit on bandwidth. For this reason, we split GSO segments into their individual packets iff the shaper is active and configured to a bandwidth <= 1 Gbps. Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk> Signed-off-by: David S. Miller <davem@davemloft.net> |
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Toke Høiland-Jørgensen
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a729b7f0bd |
sch_cake: Add overhead compensation support to the rate shaper
This commit adds configurable overhead compensation support to the rate shaper. With this feature, userspace can configure the actual bottleneck link overhead and encapsulation mode used, which will be used by the shaper to calculate the precise duration of each packet on the wire. This feature is needed because CAKE is often deployed one or two hops upstream of the actual bottleneck (which can be, e.g., inside a DSL or cable modem). In this case, the link layer characteristics and overhead reported by the kernel does not match the actual bottleneck. Being able to set the actual values in use makes it possible to configure the shaper rate much closer to the actual bottleneck rate (our experience shows it is possible to get with 0.1% of the actual physical bottleneck rate), thus keeping latency low without sacrificing bandwidth. The overhead compensation has three tunables: A fixed per-packet overhead size (which, if set, will be accounted from the IP packet header), a minimum packet size (MPU) and a framing mode supporting either ATM or PTM framing. We include a set of common keywords in TC to help users configure the right parameters. If no overhead value is set, the value reported by the kernel is used. Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk> Signed-off-by: David S. Miller <davem@davemloft.net> |
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Toke Høiland-Jørgensen
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83f8fd69af |
sch_cake: Add DiffServ handling
This adds support for DiffServ-based priority queueing to CAKE. If the shaper is in use, each priority tier gets its own virtual clock, which limits that tier's rate to a fraction of the overall shaped rate, to discourage trying to game the priority mechanism. CAKE defaults to a simple, three-tier mode that interprets most code points as "best effort", but places CS1 traffic into a low-priority "bulk" tier which is assigned 1/16 of the total rate, and a few code points indicating latency-sensitive or control traffic (specifically TOS4, VA, EF, CS6, CS7) into a "latency sensitive" high-priority tier, which is assigned 1/4 rate. The other supported DiffServ modes are a 4-tier mode matching the 802.11e precedence rules, as well as two 8-tier modes, one of which implements strict precedence of the eight priority levels. This commit also adds an optional DiffServ 'wash' mode, which will zero out the DSCP fields of any packet passing through CAKE. While this can technically be done with other mechanisms in the kernel, having the feature available in CAKE significantly decreases configuration complexity; and the implementation cost is low on top of the other DiffServ-handling code. Filters and applications can set the skb->priority field to override the DSCP-based classification into tiers. If TC_H_MAJ(skb->priority) matches CAKE's qdisc handle, the minor number will be interpreted as a priority tier if it is less than or equal to the number of configured priority tiers. Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk> Signed-off-by: David S. Miller <davem@davemloft.net> |
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Toke Høiland-Jørgensen
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ea82511518 |
sch_cake: Add NAT awareness to packet classifier
When CAKE is deployed on a gateway that also performs NAT (which is a common deployment mode), the host fairness mechanism cannot distinguish internal hosts from each other, and so fails to work correctly. To fix this, we add an optional NAT awareness mode, which will query the kernel conntrack mechanism to obtain the pre-NAT addresses for each packet and use that in the flow and host hashing. When the shaper is enabled and the host is already performing NAT, the cost of this lookup is negligible. However, in unlimited mode with no NAT being performed, there is a significant CPU cost at higher bandwidths. For this reason, the feature is turned off by default. Cc: netfilter-devel@vger.kernel.org Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk> Signed-off-by: David S. Miller <davem@davemloft.net> |
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Toke Høiland-Jørgensen
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8b7138814f |
sch_cake: Add optional ACK filter
The ACK filter is an optional feature of CAKE which is designed to improve performance on links with very asymmetrical rate limits. On such links (which are unfortunately quite prevalent, especially for DSL and cable subscribers), the downstream throughput can be limited by the number of ACKs capable of being transmitted in the *upstream* direction. Filtering ACKs can, in general, have adverse effects on TCP performance because it interferes with ACK clocking (especially in slow start), and it reduces the flow's resiliency to ACKs being dropped further along the path. To alleviate these drawbacks, the ACK filter in CAKE tries its best to always keep enough ACKs queued to ensure forward progress in the TCP flow being filtered. It does this by only filtering redundant ACKs. In its default 'conservative' mode, the filter will always keep at least two redundant ACKs in the queue, while in 'aggressive' mode, it will filter down to a single ACK. The ACK filter works by inspecting the per-flow queue on every packet enqueue. Starting at the head of the queue, the filter looks for another eligible packet to drop (so the ACK being dropped is always closer to the head of the queue than the packet being enqueued). An ACK is eligible only if it ACKs *fewer* bytes than the new packet being enqueued, including any SACK options. This prevents duplicate ACKs from being filtered, to avoid interfering with retransmission logic. In addition, we check TCP header options and only drop those that are known to not interfere with sender state. In particular, packets with unknown option codes are never dropped. In aggressive mode, an eligible packet is always dropped, while in conservative mode, at least two ACKs are kept in the queue. Only pure ACKs (with no data segments) are considered eligible for dropping, but when an ACK with data segments is enqueued, this can cause another pure ACK to become eligible for dropping. The approach described above ensures that this ACK filter avoids most of the drawbacks of a naive filtering mechanism that only keeps flow state but does not inspect the queue. This is the rationale for including the ACK filter in CAKE itself rather than as separate module (as the TC filter, for instance). Our performance evaluation has shown that on a 30/1 Mbps link with a bidirectional traffic test (RRUL), turning on the ACK filter on the upstream link improves downstream throughput by ~20% (both modes) and upstream throughput by ~12% in conservative mode and ~40% in aggressive mode, at the cost of ~5ms of inter-flow latency due to the increased congestion. In *really* pathological cases, the effect can be a lot more; for instance, the ACK filter increases the achievable downstream throughput on a link with 100 Kbps in the upstream direction by an order of magnitude (from ~2.5 Mbps to ~25 Mbps). Finally, even though we consider the ACK filter to be safer than most, we do not recommend turning it on everywhere: on more symmetrical link bandwidths the effect is negligible at best. Cc: Yuchung Cheng <ycheng@google.com> Cc: Neal Cardwell <ncardwell@google.com> Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk> Signed-off-by: David S. Miller <davem@davemloft.net> |
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Toke Høiland-Jørgensen
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7298de9cd7 |
sch_cake: Add ingress mode
The ingress mode is meant to be enabled when CAKE runs downlink of the actual bottleneck (such as on an IFB device). The mode changes the shaper to also account dropped packets to the shaped rate, as these have already traversed the bottleneck. Enabling ingress mode will also tune the AQM to always keep at least two packets queued *for each flow*. This is done by scaling the minimum queue occupancy level that will disable the AQM by the number of active bulk flows. The rationale for this is that retransmits are more expensive in ingress mode, since dropped packets have to traverse the bottleneck again when they are retransmitted; thus, being more lenient and keeping a minimum number of packets queued will improve throughput in cases where the number of active flows are so large that they saturate the bottleneck even at their minimum window size. This commit also adds a separate switch to enable ingress mode rate autoscaling. If enabled, the autoscaling code will observe the actual traffic rate and adjust the shaper rate to match it. This can help avoid latency increases in the case where the actual bottleneck rate decreases below the shaped rate. The scaling filters out spikes by an EWMA filter. Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk> Signed-off-by: David S. Miller <davem@davemloft.net> |
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Toke Høiland-Jørgensen
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046f6fd5da |
sched: Add Common Applications Kept Enhanced (cake) qdisc
sch_cake targets the home router use case and is intended to squeeze the most bandwidth and latency out of even the slowest ISP links and routers, while presenting an API simple enough that even an ISP can configure it. Example of use on a cable ISP uplink: tc qdisc add dev eth0 cake bandwidth 20Mbit nat docsis ack-filter To shape a cable download link (ifb and tc-mirred setup elided) tc qdisc add dev ifb0 cake bandwidth 200mbit nat docsis ingress wash CAKE is filled with: * A hybrid Codel/Blue AQM algorithm, "Cobalt", tied to an FQ_Codel derived Flow Queuing system, which autoconfigures based on the bandwidth. * A novel "triple-isolate" mode (the default) which balances per-host and per-flow FQ even through NAT. * An deficit based shaper, that can also be used in an unlimited mode. * 8 way set associative hashing to reduce flow collisions to a minimum. * A reasonable interpretation of various diffserv latency/loss tradeoffs. * Support for zeroing diffserv markings for entering and exiting traffic. * Support for interacting well with Docsis 3.0 shaper framing. * Extensive support for DSL framing types. * Support for ack filtering. * Extensive statistics for measuring, loss, ecn markings, latency variation. A paper describing the design of CAKE is available at https://arxiv.org/abs/1804.07617, and will be published at the 2018 IEEE International Symposium on Local and Metropolitan Area Networks (LANMAN). This patch adds the base shaper and packet scheduler, while subsequent commits add the optional (configurable) features. The full userspace API and most data structures are included in this commit, but options not understood in the base version will be ignored. Various versions baking have been available as an out of tree build for kernel versions going back to 3.10, as the embedded router world has been running a few years behind mainline Linux. A stable version has been generally available on lede-17.01 and later. sch_cake replaces a combination of iptables, tc filter, htb and fq_codel in the sqm-scripts, with sane defaults and vastly simpler configuration. CAKE's principal author is Jonathan Morton, with contributions from Kevin Darbyshire-Bryant, Toke Høiland-Jørgensen, Sebastian Moeller, Ryan Mounce, Tony Ambardar, Dean Scarff, Nils Andreas Svee, Dave Täht, and Loganaden Velvindron. Testing from Pete Heist, Georgios Amanakis, and the many other members of the cake@lists.bufferbloat.net mailing list. tc -s qdisc show dev eth2 qdisc cake 8017: root refcnt 2 bandwidth 1Gbit diffserv3 triple-isolate split-gso rtt 100.0ms noatm overhead 38 mpu 84 Sent 51504294511 bytes 37724591 pkt (dropped 6, overlimits 64958695 requeues 12) backlog 0b 0p requeues 12 memory used: 1053008b of 15140Kb capacity estimate: 970Mbit min/max network layer size: 28 / 1500 min/max overhead-adjusted size: 84 / 1538 average network hdr offset: 14 Bulk Best Effort Voice thresh 62500Kbit 1Gbit 250Mbit target 5.0ms 5.0ms 5.0ms interval 100.0ms 100.0ms 100.0ms pk_delay 5us 5us 6us av_delay 3us 2us 2us sp_delay 2us 1us 1us backlog 0b 0b 0b pkts 3164050 25030267 9530280 bytes 3227519915 35396974782 12879808898 way_inds 0 8 0 way_miss 21 366 25 way_cols 0 0 0 drops 5 0 1 marks 0 0 0 ack_drop 0 0 0 sp_flows 1 3 0 bk_flows 0 1 1 un_flows 0 0 0 max_len 68130 68130 68130 Tested-by: Pete Heist <peteheist@gmail.com> Tested-by: Georgios Amanakis <gamanakis@gmail.com> Signed-off-by: Dave Taht <dave.taht@gmail.com> Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk> Signed-off-by: David S. Miller <davem@davemloft.net> |