RE: Per queue stats

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

> From: Ferruh Yigit [mailto:ferruh.yigit@amd.com]
> Sent: Sunday, 6 October 2024 22.51
> 
> On 10/4/2024 9:40 PM, Stephen Hemminger wrote:
> > ...
> >>>>> The stats queue mapping was a feature that was hinted at being
> removed.
> >>>>> It only exists because of HW limitations on Intel ixgbe NIC and
> SW
> >>>>> limitations from RTE_ETHDEV_QUEUE_STAT_CNTRS.
> >>>>>
> >>>>
> >>>>
> >>>> We have a plan to remove 'RTE_ETHDEV_QUEUE_STAT_CNTRS', by moving
> queue
> >>>> stats to xstats.
> >>>>
> >>>> But ixgbe limitation is there.
> >>>>
> >>>>> Perhaps there should be a generic SW emulation for this the
> mapping?
> >>>>>
> >>>>
> >>>> Ack, cc'ed Bruce.
> >>>> But I am not sure ROI of the effort at this stage.
> >>>
> >>> Not sure what the specific ask for me is here. :-) Overall, I think
> moving
> >>> queue stats to xstats is the best way to go.
> >>>
> >>
> >> cc'ed because of "generic SW emulation" comment.
> >>
> >> I was thinking if this mapping can be done transparent to the user
> by
> >> driver mapping queue <-> stats_register before reading stats, but
> @Bruce
> >> let me know this won't work because the stats tracking only happens
> >> after the mapping.
> >>
> >> @Stephen, do you have something specific in your mind for SW
> emulation
> >> for mapping?
> >
> > Probably not worth doing mapping tables for SW drivers.
> >
> > My preference would be something like:
> > 	1. Introduce new API's rte_ethdev_get_queue_stats() and
> rte_ethdev_reset_queue_stats().
> >            with callbacks in ethdev ops.
> >            if driver does not support this, then do a shim in ethdev
> that uses old stats fields.
> >         2. Mark the stats mapping API's as deprecated and always
> return error.
> >            Making special case for ixgbe at this point really is not
> worth maintaining.
> >         3. After all drivers converted over, drop the fields in
> ethdev stats for queues.
> >            And fix the examples, etc. Yes this would be a big API
> change.
> >
> > Would take a year to get done (ie 25.11).
> >
> 
> The problem with existing a API, 'rte_eth_stats_get()', is it has queue
> stats fixed sized array which limits us also for some cases causes
> unnecessary memory consumption.
> 
> Our solution for now is move queue stats to xstats, as it is flexible
> this solves the problem, but as you said in other thread xstats is free
> form and may be hard for the application to use it.
> 
> One option is we can add some more data to the xstats, to help
> application to consume it easier, like number of queues just before the
> queue stats and define queue stats formatting syntax.
> 
> But if we will go with API option, instead of adding new queue stats
> ('rte_ethdev_get_queue_stats()'), we can update the existing
> 'rte_eth_stats_get()' to return dynamic number of queue stats.

Some users might not care about queue stats, so let's remove them entirely from rte_eth_stats_get(), and put them elsewhere.

> 
> And we need to find someone to own this task.
> 
> 
> Above is for queue stats, it does not solve the mapping issue, as we
> need it for a few drivers and we already have the APIs, I am for just
> keeping them as it is, they are not causing any burden to us.