Linux 5.9 To Allow Defaulting To FQ-PIE Queuing Discipline For Fighting Bufferbloat

Flow Queue Proportional Integral controller Enhanced (FQ-PIE) that has been mainline for a while in the Linux kernel's networking code will now be supported as an option for the default queuing discipline (qdisc) with the Linux 5.9 kernel.

FQ-PIE was introduced to mainline back in Linux 5.6 while with the Linux 5.9 kernel release later this year can be optionally set as the default queuing discipline scheduler. Per the commit living in net-next since the start of July, "Similar to fq_codel and the other qdiscs that can set as default, fq_pie is also suitable for general use without explicit configuration, which makes it a valid choice for this. This is useful in situations where a painless out-of-the-box solution for reducing bufferbloat is desired but fq_codel is not necessarily the best choice. For example, fq_pie can be better for DASH streaming, but there could be more cases where it's the better choice of the two simple AQMs available in the kernel."

Priority FIFO Fast remains the default queuing discipline if not override with the fair queue, controlled delay, fair queue controlled delay, stochastic fair queue, or now FQ-PIE. Those wishing to learn more about FQ-PIE in general can see this GitHub page.