Thursday 2009-08-20: SIGCOMM CONFERENCE: Performance Optimization
(Chair: Ratul Mahajan, Microsoft Research)
Session 9: Performance Optimization (Chair: Ratul Mahajan, Microsoft
Research)
———————————————————-
Safe and Effective Fine-grained TCP Retransmissions for Datacenter
Communication
Vijay Vasudevan (Carnegie Mellon University), Amar Phanishayee
(Carnegie Mellon University), Hiral Shah (Carnegie Mellon University),
Elie Krevat (Carnegie Mellon University), David Andersen (Carnegie
Mellon University), Greg Ganger (Carnegie Mellon University), Garth
Gibson (Carnegie Mellon University and Panasas, Inc), Brian Mueller
(Panasas, Inc.)
———————————————————-
TCP has a problem in data centers: the dropped packet takes 200ms to be
retransmitted
There are some apps that can not tolerate that
solution: enable ms retransmission
improve throughout/latency in datacenter
safe for wide-area
10-100 microsecond, 1-10Gbps
under heavy load, pkt loss is common
1 TCP timout is 1000s times more than RTT
The scenario involves the client sending a single request packet
once in a while. This is in contrary of TCP design principles: full
window of packets. Hence, the fast-retransmission does not get
triggered in case of pkt loss
Solution:
1) eliminate long 200ms timeout
2) TCP must track RTT in microseconds
Interaction with delayed ACK
- The reduction is not so much
Stability? Causing congestion collapse?
- Today’s TCP has mechanisms to cope with that
Q: problem for congestion control?
A: exponential backup takes care of that
Tags: Sigcomm09
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