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

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

> -----Original Message-----
> From: Jerin Jacob [mailto:jerin.jacob@caviumnetworks.com]
> Sent: Monday, October 30, 2017 12:38 PM
> To: Eads, Gage <gage.eads@intel.com>
> Cc: dev@dpdk.org; Richardson, Bruce <bruce.richardson@intel.com>; Van
> Haaren, Harry <harry.van.haaren@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: Re: [dpdk-dev] [PATCH] eventdev: remove experimental label
> 
> -----Original Message-----
> > Date: Mon, 23 Oct 2017 18:27:52 +0000
> > From: "Eads, Gage" <gage.eads@intel.com>
> > To: Jerin Jacob <jerin.jacob@caviumnetworks.com>, "dev@dpdk.org"
> >  <dev@dpdk.org>
> > CC: "Richardson, Bruce" <bruce.richardson@intel.com>, "Van Haaren, Harry"
> >  <harry.van.haaren@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: RE: [dpdk-dev] [PATCH] eventdev: remove experimental label
> >
> > Hi Jerin,
> 
> Hi Gage,
> 
> >
> > 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.
> 
> 
> 
> The HW implementations, I know, it does the implicit release. Otherwise it
> will result in deadlock because it cannot hold reordering metadata for
> the longtime(SRAM is limited etc)
> 
> Coming back to cryptodev use case, if I understand it correctly, before
> application enqueues to crypto queue, the application will change the tag and
> submit to ATOMIC queue. So as long as crypto queue competes for the
> crypto work in order then the order will be maintained.
> 
> In typical outbound IPSec use case,
> - Stage 1 will be processed in ORDERED where application does the SA
>   lookup
> - Once SA found, application enqueue to ATOMIC stage with SA as flow_id.
> - When the event comes from the ATOMIC queue, it in ingress order and
>   then it submits to the crypto queue
> - Crypto queue maintains the FIFO order.
> - On IPSec crypto work competition, packets will come in Stage 3.
> - So at Stage 3, packets are in ingress order for the given SA flow id.
>                                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 
> Having said that, If SW implementation needs to do differently for performance
> reasons then we will end up in capability as HW implementation works in the
> implicit release. May we can sort out through capability or separate adapter for
> crypto case. But I think, those will be new additions to the API.So removing the
> experimental tags may be OK.
> But if you have strong opinion on keeping the experimental tag till we address
> the crypto use case then I am fine with that.
> 
> Thoughts?

Ok, agreed, no need to keep the tag for this concern. The capability idea is intriguing -- I'll chew on this and we can tackle it at a later point.

Thanks,
Gage

> 
> Jerin
> 
> 
> >
> > Thanks,
> > Gage
> >