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Karrq
approved these changes
Feb 24, 2026
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Problem
DRR (Deficit Round Robin) has a fundamental head-of-line blocking interaction with netem that causes high-delay destinations to block low-delay destinations.
DRR's dequeue() peeks at the first active class. Netem (a non-work-conserving qdisc) returns NULL when the configured delay hasn't elapsed yet. DRR sees NULL and immediately returns without trying other classes. This is a kernel-level issue with no userspace workaround.
Proposed change
Replaced DRR with HTB as the root classful qdisc. HTB's dequeue() correctly handles non-work-conserving children: when a child returns NULL, it advances to the next class instead of giving up.