cake default target is too low for bbr?

Andy Furniss adf.lists at gmail.com
Fri Apr 28 15:03:14 EDT 2017


Motivated by an observation about steam downloads in the thread Getting
Cake to work better with Steam and similar applications I set up a test
- maybe not the best test ever but interesting results.

Put cake on ifb on PC with netem also on egress/ingress adding 4ms each
way (that's how close I am to steam).

Pretend I have 16mbit atm, though here it's shaped on egress and I am
sending 5 connections 10 sec with netperf and bbr enabled.

This doesn't happen with cubic.

OK so ecn may cure - but people may no know how or want that on.

This issue is that there are a lot of drops causing someone with a
highly asymmetric line to possibly use all upload as (s)ack per packet
is prevalent due to excessive drops.

Here's some pastes same test with target varied (via rtt param)
The 5 connections are from different src ips.

qdisc cake 1: dev ifb0 root refcnt 2 bandwidth 16Mbit diffserv3 
dual-srchost rtt 100.0ms atm overhead 40 via-ethernet
  Sent 17477050 bytes 11597 pkt (dropped 8476, overlimits 31565 requeues 0)
  backlog 0b 0p requeues 0
  memory used: 144Kb of 4Mb
  capacity estimate: 16Mbit
                  Bulk   Best Effort      Voice
   thresh         1Mbit      16Mbit       4Mbit
   target        18.2ms       5.0ms       5.0ms
   interval     113.2ms     100.0ms      10.0ms
   pk_delay         0us       6.9ms         0us
   av_delay         0us       4.6ms         0us
   sp_delay         0us         5us         0us
   pkts               0       20073           0
   bytes              0    30307578           0
   way_inds           0           0           0
   way_miss           0          10           0
   way_cols           0           0           0
   drops              0        8476           0
   marks              0           0           0
   sp_flows           0           5           0
   bk_flows           0           1           0
   un_flows           0           0           0
   max_len            0        1514           0


qdisc cake 1: dev ifb0 root refcnt 2 bandwidth 16Mbit diffserv3 
dual-srchost rtt 200.0ms atm overhead 40 via-ethernet
  Sent 17459144 bytes 11584 pkt (dropped 3277, overlimits 26349 requeues 0)
  backlog 0b 0p requeues 0
  memory used: 161280b of 4Mb
  capacity estimate: 16Mbit
                  Bulk   Best Effort      Voice
   thresh         1Mbit      16Mbit       4Mbit
   target        18.2ms      10.0ms      10.0ms
   interval     208.2ms     200.0ms      20.0ms
   pk_delay         0us      12.7ms         0us
   av_delay         0us      10.3ms         0us
   sp_delay         0us        11us         0us
   pkts               0       14861           0
   bytes              0    22420426           0
   way_inds           0           0           0
   way_miss           0          10           0
   way_cols           0           0           0
   drops              0        3277           0
   marks              0           0           0
   sp_flows           0           5           0
   bk_flows           0           1           0
   un_flows           0           0           0
   max_len            0        1514           0

qdisc cake 1: dev ifb0 root refcnt 2 bandwidth 16Mbit diffserv3 
dual-srchost rtt 300.0ms atm overhead 40 via-ethernet
  Sent 17613408 bytes 11680 pkt (dropped 1574, overlimits 24849 requeues 0)
  backlog 0b 0p requeues 0
  memory used: 171Kb of 4Mb
  capacity estimate: 16Mbit
                  Bulk   Best Effort      Voice
   thresh         1Mbit      16Mbit       4Mbit
   target        18.2ms      15.0ms      15.0ms
   interval     303.2ms     300.0ms      30.0ms
   pk_delay         0us      13.6ms         0us
   av_delay         0us      12.1ms         0us
   sp_delay         0us        14us         0us
   pkts               0       13254           0
   bytes              0    19996444           0
   way_inds           0           0           0
   way_miss           0          10           0
   way_cols           0           0           0
   drops              0        1574           0
   marks              0           0           0
   sp_flows           0           5           0
   bk_flows           0           1           0
   un_flows           0           0           0
   max_len            0        1514           0


qdisc cake 1: dev ifb0 root refcnt 2 bandwidth 16Mbit diffserv3 
dual-srchost rtt 400.0ms atm overhead 40 via-ethernet
  Sent 17674640 bytes 11720 pkt (dropped 920, overlimits 24270 requeues 0)
  backlog 0b 0p requeues 0
  memory used: 186624b of 4Mb
  capacity estimate: 16Mbit
                  Bulk   Best Effort      Voice
   thresh         1Mbit      16Mbit       4Mbit
   target        20.0ms      20.0ms      20.0ms
   interval     400.0ms     400.0ms      40.0ms
   pk_delay         0us      16.8ms         0us
   av_delay         0us      16.2ms         0us
   sp_delay         0us        17us         0us
   pkts               0       12640           0
   bytes              0    19067520           0
   way_inds           0           0           0
   way_miss           0          10           0
   way_cols           0           0           0
   drops              0         920           0
   marks              0           0           0
   sp_flows           0           5           0
   bk_flows           0           1           0
   un_flows           0           0           0
   max_len            0        1514           0


qdisc cake 1: dev ifb0 root refcnt 2 bandwidth 16Mbit diffserv3 
dual-srchost rtt 500.0ms atm overhead 40 via-ethernet
  Sent 17614080 bytes 11680 pkt (dropped 613, overlimits 23885 requeues 0)
  backlog 0b 0p requeues 0
  memory used: 186624b of 4Mb
  capacity estimate: 16Mbit
                  Bulk   Best Effort      Voice
   thresh         1Mbit      16Mbit       4Mbit
   target        25.0ms      25.0ms      25.0ms
   interval     500.0ms     500.0ms      50.0ms
   pk_delay         0us      18.6ms         0us
   av_delay         0us      17.1ms         0us
   sp_delay         0us        19us         0us
   pkts               0       12293           0
   bytes              0    18542162           0
   way_inds           0           0           0
   way_miss           0          10           0
   way_cols           0           0           0
   drops              0         613           0
   marks              0           0           0
   sp_flows           0           5           0
   bk_flows           0           1           0
   un_flows           0           0           0
   max_len            0        1514           0


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