Re: [PATCH net-next 2/2] net: dsa: mv88e6xxx: implement egress tbf qdisc for 6393x family

[Alexis Lothoré]

On 6/9/23 19:16, Andrew Lunn wrote:
>> Yes, I can do that (or maybe -EINVAL to match Vladimir's comment ?). I think
>> it's worth mentioning that I encountered an issue regarding those values during
>> tests: I use tc program to set the tbf, and I observed that tc does not even
>> reach kernel to set the qdisc if we pass no burst/latency value OR if we set it
>> to 0. So tc enforces right on userspace side non-zero value for those
>> parameters, and I have passed random values and ignored them on kernel side.
> 
> That is not good. Please take a look around and see if any other
> driver offloads TBF, and what they do with burst.
> 
>> Checking available doc about tc-tbf makes me feel like that indeed a TBF qdisc
>> command without burst or latency value makes no sense, except my use case can
>> not have such values. That's what I struggled a bit to find a proper qdisc to
>> match hardware cap. I may fallback to a custom netlink program to improve testing.
> 
> We don't really want a custom application, since we want users to use
> TC to set this up.
> 
> Looking at the 6390 datasheet, Queue Counter Registers, mode 8 gives
> the number of egress buffers for a port. You could validate that the
> switch has at least the requested number of buffers assigned to the
> port? There is quite a bit you can configure, so maybe there is a way
> to influence the number of buffers, so you can actually implement the
> burst parameter?

Thanks for the pointers. I will check the egress buffers configuration and see
if I can come up with something better

> 
>       Andrew

-- 
Alexis Lothoré, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com