Re: [dpdk-dev] [PATCH] eventdev: remove experimental label

["Eads, Gage" <gage.eads@intel.com>]

Hi Jerin,

I have one concern with the API that may delay changing the label.

The implicit release that in rte_event_dequeue_burst() is a problem when using asynchronous/look-aside hardware, like a cryptodev. For instance, let's say in pipeline stage N the worker takes the event's mbuf and places it in a per-worker crypto request queue. When the worker next calls rte_event_dequeue_burst(), that function will release the previous event which could cause the flow to migrate to another worker, and this could result in packet reordering.

To prevent this, the worker can't call dequeue until the look-aside operation completes...in effect treating the asynchronous/look-aside hardware as synchronous. Another option is to feed stage N's queue to a single port to avoid the flow migration, but that port may become a bottleneck.

We could remove the implicit release functionality or add a port configuration flag to disable it, so the default behavior is unchanged. Removing it will completely will likely require changes in existing code, but it simplifies the usage model (all dequeued events must be either forwarded or released) and the PMD's dequeue code. This functionality could be removed from the software eventdev fairly easily, but I haven't looked into the hardware PMDs.

Thanks,
Gage

> -----Original Message-----
> From: Jerin Jacob [mailto:jerin.jacob@caviumnetworks.com]
> Sent: Monday, October 16, 2017 5:33 AM
> To: dev@dpdk.org
> Cc: Jerin Jacob <jerin.jacob@caviumnetworks.com>; Richardson, Bruce
> <bruce.richardson@intel.com>; Van Haaren, Harry
> <harry.van.haaren@intel.com>; Eads, Gage <gage.eads@intel.com>; Hemant
> Agrawal <hemant.agrawal@nxp.com>; Nipun Gupta <nipun.gupta@nxp.com>;
> Rao, Nikhil <nikhil.rao@intel.com>; Pavan Nikhilesh
> <pbhagavatula@caviumnetworks.com>; Thomas Monjalon
> <thomas@monjalon.net>
> Subject: [dpdk-dev] [PATCH] eventdev: remove experimental label
> 
> The eventdev API was introduced in DPDK 17.05 release.
> Since then it
> - has been reviewed and iterated for 17.08, 17.11 releases
> - three drivers were implemented using the API.
> - introduced another subsystem like service core and ethdev-eventdev Rx
> adapter APIs to abstract the difference between HW and SW eventdev
> implementations in a transparent way.
> - had extensive use by the app/test-eventdev/ and
> examples/eventdev_pipeline_sw_pmd/
> 
> I believe the API is now stable and the EXPERIMENTAL label should be removed.
> 
> CC: Bruce Richardson <bruce.richardson@intel.com>
> CC: Harry van Haaren <harry.van.haaren@intel.com>
> CC: Gage Eads <gage.eads@intel.com>
> CC: Hemant Agrawal <hemant.agrawal@nxp.com>
> CC: Nipun Gupta <nipun.gupta@nxp.com>
> CC: Nikhil Rao <nikhil.rao@intel.com>
> CC: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>
> CC: Thomas Monjalon <thomas@monjalon.net>
> Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> ---
> 
> There are two more outstanding eventdev API changes. Please find below.
> Please express if you have any concern in changing those APIs. I would
> like to fix this API issue and remove experimental tag in v17.11,
> if we all agree.
> 
> - evendev: fix inconsistency in event queue config
> http://dpdk.org/dev/patchwork/patch/30293/
> - remove rte_event_schedule() API and use service core infrastructure
> http://dpdk.org/dev/patchwork/patch/30375/
> 
> ---
>  MAINTAINERS | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 2a58378b7..4a4be3a54 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -262,7 +262,7 @@ F: lib/librte_cryptodev/
>  F: test/test/test_cryptodev*
>  F: examples/l2fwd-crypto/
> 
> -Eventdev API - EXPERIMENTAL
> +Eventdev API
>  M: Jerin Jacob <jerin.jacob@caviumnetworks.com>
>  T: git://dpdk.org/next/dpdk-next-eventdev
>  F: lib/librte_eventdev/
> --
> 2.14.2