Re: [RFC net-next 2/2] ipv6: ioam: Support for Buffer occupancy data field

[Justin Iurman <justin.iurman@uliege.be>]

On Dec 21, 2021, at 6:23 PM, Vladimir Oltean olteanv@gmail.com wrote:
> I know nothing about OAM and therefore did not want to comment, but I

NP, all opinions are more than welcome.

> think the point raised about the metric you propose being irrelevant in
> the context of offloaded data paths is quite important. The "devlink-sb"
> proposal was dismissed very quickly on grounds of requiring sleepable
> context, is that a deal breaker, and if it is, why? Not only offloaded

Can't sleep in the datapath.

> interfaces like switches/routers can report buffer occupancy. Plain NICs
> also have buffer pools, DMA RX/TX rings, MAC FIFOs, etc, that could
> indicate congestion or otherwise high load. Maybe slab information could

Indeed. Is there any API to retrieve such metric? Anyway, that would
probably involve (again) sleepable context.

> be relevant, for lack of a better option, on virtual interfaces, but if
> they're physical, why limit ourselves on reporting that? The IETF draft
> you present says "This field indicates the current status of the
> occupancy of the common buffer pool used by a set of queues." It appears
> to me that we could try to get a reporting that has better granularity
> (per interface, per queue) than just something based on
> skbuff_head_cache. What if someone will need that finer granularity in
> the future.

I think we all agree (Jakub, you, and I) on this point. The thing is,
what could be a better solution to have something generic that makes
sense, instead of just nothing? Is it actually feasible at all?