TC(8) Linux TC(8)
drr - deficit round robin scheduler
tc qdisc ... add drr [ quantum bytes ]
The Deficit Round Robin Scheduler is a classful queuing discipline as a more flexible replacement for Stochastic Fairness Queuing. Unlike SFQ, there are no built-in queues -- you need to add classes and then set up filters to classify packets accordingly. This can be useful e.g. for using RED qdiscs with different settings for particular traffic. There is no default class -- if a packet cannot be classified, it is dropped.
Each class is assigned a deficit counter, initialized to quantum. DRR maintains an (internal) ''active'' list of classes whose qdiscs are non-empty. This list is used for dequeuing. A packet is dequeued from the class at the head of the list if the packet size is smaller or equal to the deficit counter. If the counter is too small, it is increased by quantum and the scheduler moves on to the next class in the active list.
quantum Amount of bytes a flow is allowed to dequeue before the scheduler moves to the next class. Defaults to the MTU of the interface. The minimum value is 1.
To attach to device eth0, using the interface MTU as its quantum: # tc qdisc add dev eth0 handle 1 root drr Adding two classes: # tc class add dev eth0 parent 1: classid 1:1 drr # tc class add dev eth0 parent 1: classid 1:2 drr You also need to add at least one filter to classify packets. # tc filter add dev eth0 protocol .. classid 1:1 Like SFQ, DRR is only useful when it owns the queue -- it is a pure scheduler and does not delay packets. Attaching non-work- conserving qdiscs like tbf to it does not make sense -- other qdiscs in the active list will also become inactive until the dequeue operation succeeds. Embed DRR within another qdisc like HTB or HFSC to ensure it owns the queue. You can mimic SFQ behavior by assigning packets to the attached classes using the flow filter: tc qdisc add dev .. drr for i in .. 1024;do tc class add dev .. classid $handle:$(print %x $i) tc qdisc add dev .. fifo limit 16 done tc filter add .. protocol ip .. $handle flow hash keys src,dst,proto,proto-src,proto-dst divisor 1024 perturb 10
o M. Shreedhar and George Varghese "Efficient Fair Queuing using Deficit Round Robin", Proc. SIGCOMM 95.
This implementation does not drop packets from the longest queue on overrun, as limits are handled by the individual child qdiscs.
tc(8), tc-htb(8), tc-sfq(8)
sched_drr was written by Patrick McHardy.
This page is part of the iproute2 (utilities for controlling TCP/IP networking and traffic) project. Information about the project can be found at ⟨http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2⟩. If you have a bug report for this manual page, send it to firstname.lastname@example.org, email@example.com. This page was obtained from the project's upstream Git repository ⟨https://git.kernel.org/pub/scm/network/iproute2/iproute2.git⟩ on 2021-04-01. (At that time, the date of the most recent commit that was found in the repository was 2021-03-22.) If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up-to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which is not part of the original manual page), send a mail to firstname.lastname@example.org iproute2 January 2010 TC(8)
Pages that refer to this page: tc(8), tc-ets(8)