RE: [PATCH v3 0/7] introduce per-queue limit watermark and host shaper

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Thomas Monjalon [mailto:thomas@monjalon.net]
> Sent: Tuesday, 24 May 2022 17.59
> 
> +Cc people involved in previous versions
> 
> 24/05/2022 17:20, Spike Du:
> > LWM(limit watermark) is per RX queue attribute, when RX queue
> fullness reach the LWM limit, HW sends an event to dpdk application.
> > Host shaper can configure shaper rate and lwm-triggered for a host
> port.

Please ignore this comment, it is not important, but I had to get it out of my system: I assume that the "LWM" name is from the NIC datasheet; otherwise I would probably prefer something with "threshold"... LWM is easily confused with "low water mark", which is the opposite of what the LWM does. Names are always open for discussion, so I won't object to it.

> > The shaper limits the rate of traffic from host port to wire port.

From host to wire? It is RX, so you must mean from wire to host.

> > If lwm-triggered is enabled, a 100Mbps shaper is enabled
> automatically when one of the host port's Rx queues receives LWM event.
> >
> > These two features can combine to control traffic from host port to
> wire port.

Again, you mean from wire to host?

> > The work flow is configure LWM to RX queue and enable lwm-triggered
> flag in host shaper, after receiving LWM event, delay a while until RX
> queue is empty , then disable the shaper. We recycle this work flow to
> reduce RX queue drops.

You delay while RX queue gets drained by some other threads, I assume.

Surely, the excess packets must be dropped somewhere, e.g. by the shaper?

> >
> > Add new libethdev API to set LWM, add rte event
> RTE_ETH_EVENT_RXQ_LIMIT_REACHED to handle LWM event.

Makes sense to make it public; could be usable for other purposes, similar to interrupt coalescing, as mentioned by Stephen.

> > For host shaper,
> because it doesn't align to existing DPDK framework and is specific to
> Nvidia NIC, use PMD private API.

Makes sense to keep it private.

> >
> > For integration with testpmd, put the private cmdline function and
> LWM event handler in mlx5 PMD directory by adding a new file
> mlx5_test.c. Only add minimal code in testpmd to invoke interfaces from
> mlx5_test.c.
> >
> > Spike Du (7):
> >   net/mlx5: add LWM support for Rxq
> >   common/mlx5: share interrupt management
> >   ethdev: introduce Rx queue based limit watermark
> >   net/mlx5: add LWM event handling support
> >   net/mlx5: support Rx queue based limit watermark
> >   net/mlx5: add private API to config host port shaper
> >   app/testpmd: add LWM and Host Shaper command
> >