Deficit round robin

Deficit round robin (DRR)^[1], also deficit weighted round robin (DWRR), is a modified weighted round robin scheduling discipline. DRR was proposed by M. Shreedhar and G. Varghese in 1995. It can handle packets of variable size without knowing their mean size. A maximum packet size number is subtracted from the packet length, and packets that exceed that number are held back until the next visit of the scheduler.

WRR serves every nonempty queue whereas DRR serves packets at the head of every nonempty queue which deficit counter is greater than the packet's size. If it is lower then deficit counter is increased by some given value called quantum. Deficit counter is decreased by the size of packets being served.

Compared with Fair queueing (FQ) scheduler that has complexity of O(log(n)) (n is the number of active flows), the complexity of DRR is O(1).

See also

• scheduling disciplines

References

External links

• UC Berkeley EE122 lecture: Efficient fair queueing using deficit round robin