[dpdk-dev] [v1] ethdev: support Tx queue used count

[Stephen Hemminger]

On Fri, 12 Jan 2024 12:31:27 +0530
Jerin Jacob <jerinjacobk at gmail.com> wrote:

> >
> > Has anyone investigated implementing dynamic tx queue limits like
> > Linux BQL?  
> 
> In DPDK APIs, it can expressed through creating correct TM
> topology(shaping or rate limiting) via rte_tm API

That won't work for BQL.
Byte Queue Limits measures the latency for transmit queue.
A counter is started when packets are queued to hardware and
decremented when they are done transmitting. This is then fed
back into the transmit logic; the concept is too eliminate bufferbloat
in the transmit side by providing early feedback up the stack.

Doing BQL needs a mechanism to know when packets are sent,
either in ethdev or in every device driver.

Right now it is common for applications to have very large
worse case transmit queue length (descriptors) and that introduces
latency.