Re: [PATCH net-next V2 2/3] net/mlx5e: Add device PCIe congestion ethtool stats

[Tariq Toukan <ttoukan.linux@gmail.com>]

On 14/07/2025 18:26, Jakub Kicinski wrote:
> On Sat, 12 Jul 2025 07:55:27 +0000 Dragos Tatulea wrote:
>>> The metrics make sense, but utilization has to be averaged over some
>>> period of time to be meaningful. Can you shad any light on what the
>>> measurement period or algorithm is?
>>
>> The measurement period in FW is 200 ms.
> 
> SG, please include in the doc.
>   
>>>> +	changes = cong_event->state ^ new_cong_state;
>>>> +	if (!changes)
>>>> +		return;
>>>
>>> no risk of the high / low events coming so quickly we'll miss both?
>> Yes it is possible and it is fine because short bursts are not counted. The
>> counters are for sustained high PCI BW usage.
>>
>>> Should there be a counter for "mis-firing" of that sort?
>>> You'd be surprised how long the scheduling latency for a kernel worker
>>> can be on a busy server :(
>>>   
>> The event is just a notification to read the state from FW. If the
>> read is issued later and the state has not changed then it will not be
>> considered.
> 
> 200ms is within the range of normal scheduler latency on a busy server.
> It's not a deal breaker, but I'd personally add a counter for wakeups
> which did not result in any state change. Likely recent experience
> with constant EEVDF regressions and sched_ext is coloring my judgment.
> 

NP with that.
We'll add it as a followup patch, after it's implemented and properly 
tested.

Same applies for the requested devlink config (replacing the sysfs).

For now, I'll respin without the configuration part and the extra counter.