1 Outline What is bufferbloat? Bufferbloat mitigation in - - PowerPoint PPT Presentation
1 Outline What is bufferbloat? Bufferbloat mitigation in Linux Fixing bloat in the WiFi stack Airtime fairness and policy Status of mainline drivers Future / ongoing work - Toke Hiland-Jrgensen
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10 20 30 40 50 60 70 Time (s) 200 400 600 800 Latency (ms)
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Supply line Flus h valve Filler tube Inlet valve Float
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k pkts
Timestamp
now - timestamp > 5ms?
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20 40 60 80 100 Mean induced latency (ms) 8.8 8.9 9.0 9.1 9.2 9.3 9.4 9.5 9.6 Mean TCP goodput (Mbit/s) pfifo_fast ared pie codel sfq fq_nocodel fq_codel
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A->A A->B A->C A->C B->C B->D A->A A->B A->C A->C B->C B->D A->A A->B A->C A->C B->C B->D A->A A->B A->C A->C B->C B->D A->A A->B A->C A->C B->C B->D 0.0 0.5 1.0 1.5 2.0 2.5 Mbits/s cake cake_dst cake_src cake_triple fq_codel
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50 100 150 200 250 300 350 Mean induced latency (ms) 10 20 30 40 50 60 Mean TCP goodput (Mbit/s) pfifo_fast pfifo_fast ared ared pie pie codel codel sfq sfq fq_nocodel fq_nocodel fq_codel fq_codel
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1000 *
Qdisc layer MAC layer ath9k driver
*Can be replaced with an arbitrary configuration
Per HW queue (x4) 2 aggr
FIFO
FIFO*
buf_q retry_q TID 123
Prio
buf_q retry_q
TID RR Assign TID
Retries To hardware 123
Prio
Qdisc layer (bypassed) MAC layer ath9k driver HW queue (x4)
2 aggr FIFO RR Assign TID Retries
To hardware
retry_q TID Prio Split flows 8192 (Global limit) retry_q TID
FQ-
CoDel
Prio Split flows 8192 (Global limit)
FQ-
CoDel
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With our solution Without our solution
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1 |I| T_data(i) ∑ _j∈IT_data(j)
L_i T_data(i)+T_oh
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Kernel mac80211 subsystem Weighted DRR scheduler WiFi hardware Device driver Userspace Policy daemon Assoc / disassoc notifications Station queue state Set station weights Airtime usage Station
Weight Deficits
Station
Weight Deficits
Station
Weight Deficits User configuration Station state tracker
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10 20 30 40 Time (s) 0.00 0.25 0.50 0.75 1.00 Airtime share 10 20 30 40 Time (s) 0.00 0.25 0.50 0.75 1.00 Airtime share
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