Bufferbloat: why latency rises under load

If latency is normal while idle but rises sharply during a busy upload or download, bufferbloat may be the cause: queues at the bottleneck are holding packets for too long.

What bufferbloat looks like

Bufferbloat is excessive latency caused by persistently large queues, often visible when an upload or download saturates a bottleneck. More throughput alone does not describe or necessarily solve queueing delay.

How to test latency under load

Measure latency while the connection is idle, then repeat while saturating upload and download. A large latency increase under load is the useful signal. Queue management such as SQM can help when the bottleneck is under your control. You can compare throughput before and after a change with the 2ip speed test.

What you can do about it

Technical reference: RFC 7567.