BQL enabled drivers

Queue Disciplines such as fq_codel and fq need the underlying buffering of the device and device driver well controlled. Under Linux, the mechanism to do so is called "Byte Queue Limits" (BQL), which needs a small amount of driver support to enable.

This is a partial list of the known BQL-enabled device drivers for Linux as of version 3.14

  • Intel e1000e, e1000, ixgbe, ivb40evf,i40e
  • Atheros ar71xx
  • Nvidia forcedeath
  • Marvell sky2, skge
  • Broadcom bnx2, tg3, b44
  • Mellanox mlx4
  • Freescale gianfar
  • Realtek 8139
  • Isilicon hix5hd2

Highly desirable to BQL enable

  • Cisco, AMD, Xilinx and other manufacturers
  • Kirkwood (dreamplug, guruplug etc)
  • net-usb (patch discussed on cerowrt-devel) (raspery pi uses usb to network)
  • r8169 (buggy in 3.6 and earlier, currently reverted)
  • niu (same problem basically as r8169, also currently reverted)

There are 7 out of tree BQL drivers here that could use testing and integration: http://www.mcmilk.de/projects/linux-bql/

Other subsystems

BQL is desirable for devices running at line rate. It is not required for soft rate shapers such as hfsc and htb, which are independent of the underlying wire rate.

Similar techniques to BQL could be used at other layers in the stack, such as various forms of wireless, usb network devices, and adsl. But adding this technique is going to be really hard for wireless .