[dpdk-dev] [PATCH v3 3/6] power: add simple power management API and callback

[Stephen Hemminger]

On Fri,  4 Sep 2020 11:18:57 +0100
Liang Ma <liang.j.ma at intel.com> wrote:

> Add a simple on/off switch that will enable saving power when no
> packets are arriving. It is based on counting the number of empty
> polls and, when the number reaches a certain threshold, entering an
> architecture-defined optimized power state that will either wait
> until a TSC timestamp expires, or when packets arrive.
> 
> This API is limited to 1 core 1 port 1 queue use case as there is
> no coordination between queues/cores in ethdev. 1 port map to multiple
> core will be supported in next version.

The common way to express is this is:

This API is not thread-safe and not preempt-safe.
There is also no mechanism for a single thread to wait on multiple queues.

> 
> This design leverage RX Callback mechnaism which allow three
> different power management methodology co exist.

nit coexist is one word

> 
> 1. umwait/umonitor:
> 
>    The TSC timestamp is automatically calculated using current
>    link speed and RX descriptor ring size, such that the sleep
>    time is not longer than it would take for a NIC to fill its
>    entire RX descriptor ring.
> 
> 2. Pause instruction
> 
>    Instead of move the core into deeper C state, this lightweight
>    method use Pause instruction to releaf the processor from
>    busy polling.

Wording here is a problem, and "releaf" should be "relief"?
Rewording into active voice grammar would be easier.

     Use Pause instruction to allow processor to go into deeper C
     state when busy polling.



> 
> 3. Frequency Scaling
>    Reuse exist rte power library to scale up/down core frequency
>    depend on traffic volume.