[EXT] Re: [PATCH 1/2] doc: add enqueue depth for new event type

[Thomas Monjalon]

14/07/2022 18:57, Van Haaren, Harry:
> > -----Original Message-----
> > From: Van Haaren, Harry
> > Sent: Thursday, July 14, 2022 5:54 PM
> > To: Pavan Nikhilesh Bhagavatula <pbhagavatula at marvell.com>; mattias.ronnblom
> > <mattias.ronnblom at ericsson.com>; Thomas Monjalon <thomas at monjalon.net>
> > Cc: Jerin Jacob Kollanukkaran <jerinj at marvell.com>; Ray Kinsella <mdr at ashroe.eu>;
> > dev at dpdk.org; McDaniel, Timothy <timothy.mcdaniel at intel.com>; Hemant
> > Agrawal <hemant.agrawal at nxp.com>; sachin.saxena at oss.nxp.com;
> > liangma at liangbit.com; Mccarthy, Peter <Peter.Mccarthy at intel.com>; Carrillo, Erik
> > G <Erik.G.Carrillo at intel.com>; Gujjar, Abhinandan S
> > <abhinandan.gujjar at intel.com>; Jayatheerthan, Jay <jay.jayatheerthan at intel.com>;
> > Burakov, Anatoly <anatoly.burakov at intel.com>
> > Subject: RE: [EXT] Re: [PATCH 1/2] doc: add enqueue depth for new event type
> > 
> > > -----Original Message-----
> > > From: Pavan Nikhilesh Bhagavatula <pbhagavatula at marvell.com>
> > > Sent: Thursday, July 14, 2022 5:42 PM
> > > To: mattias.ronnblom <mattias.ronnblom at ericsson.com>; Thomas Monjalon
> > > <thomas at monjalon.net>
> > > Cc: Jerin Jacob Kollanukkaran <jerinj at marvell.com>; Ray Kinsella
> > <mdr at ashroe.eu>;
> > > dev at dpdk.org; McDaniel, Timothy <timothy.mcdaniel at intel.com>; Hemant
> > > Agrawal <hemant.agrawal at nxp.com>; sachin.saxena at oss.nxp.com;
> > > liangma at liangbit.com; Mccarthy, Peter <peter.mccarthy at intel.com>; Van
> > Haaren,
> > > Harry <harry.van.haaren at intel.com>; Carrillo, Erik G <erik.g.carrillo at intel.com>;
> > > Gujjar, Abhinandan S <abhinandan.gujjar at intel.com>; Jayatheerthan, Jay
> > > <jay.jayatheerthan at intel.com>; Burakov, Anatoly <anatoly.burakov at intel.com>
> > > Subject: RE: [EXT] Re: [PATCH 1/2] doc: add enqueue depth for new event type
> > 
> > <snip old conversation>
> > 
> > > > >> If the underlying hardware has some limitations,
> > > > >> why not let the driver loop until back pressure occurs? Then you can
> > > >
> > > > You didn't answer this question. Why not let the driver loop, until you
> > > > for some reason or the other can't accept more events?
> > >
> > > CNXK event driver cannot accept forwarding(enq) more than one event that has
> > > been dequeued. Enqueueing more than one event for forwarding/releasing
> > > is a violation from HW perspective, this is currently announced by BURST
> > capability.
> > > But It can enqueue a burst if new events.
> > 
> > Can't the driver just backpressure NEW events? that's what the event/sw driver
> > does in order to limit "new" inflight events. App attempts to enq FWD/REL, no
> > problem. App enqueues burst of NEW (and there's only N spaces) then the
> > first N events pass, and the rest are returned to the application.
> > 
> > > If you see the current example implementation we pick the worker based on
> > > BURST capability for optimizing the enqueue/dequeue by providing a hint
> > > to the driver layer.
> > 
> > Please provide a link to the code? Others are not familiar with the CNXK driver,
> > or the sample code you're referring to...
> > 
> > 
> > > Although, we could live with aggregating the events at driver layer based on
> > > queue. We would still require announce burst capability for new events i.e.
> > > changes to the info structure.
> > 
> > As per above, I still don't see a reason why this HW optimization/limitation
> > needs to be pushed to the application layer. Why can the driver not handle
> > things by allowing/backpressure to the events it can/can't handle?
> > 
> > 
> > In this email thread[1] you've suggested reworking the rx_burst API with a
> > flag to indicate "same destination". This still pushes the problem to the application,
> > and exposes more HW/PMD specific options. This impl is *slightly* better because it
> > wont' require new APIs for each mode, but also *breaks all existing apps*!?
> > 
> > I'm just not understanding why the application needs to change, and why it
> > cannot be optimized/handled in the driver layer.
> > 
> > [1] http://mails.dpdk.org/archives/dev/2022-July/246717.html
> > 
> > <snip old conversation>
> 
> 
> Let me be very clear, but also try to help here;
>   I'm not in favour of the changes as proposed here, and feel that pushing
>   the problem to Application API is NOT the right solution.
> 
> But *just in case* there is a *genuine* reason that we need an API/ABI
> change, and that can be justified clearly in the upcoming weeks, then I'd
> prefer not have problems with the deprecation notice not being included.
> 
> This Ack is *only* to allow possible API/ABI changes in 22.11, and not for
> the proposal above.
> 
> Acked-by: Harry van Haaren <harry.van.haaren at intel.com>

It doesn't make sense to add a deprecation notice
if the direction is not agreed.

Let's discuss further and ask for techboard help if needed.
In general, I would not be surprised that it's time for a cleanup in this API.