Re: [dpdk-dev] [PATCH] compressdev: add feature flag to specify where processing is done

["De Lara Guarch, Pablo" <pablo.de.lara.guarch@intel.com>]

Hi Shally,

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Trahe, Fiona
> Sent: Wednesday, December 19, 2018 5:10 PM
> To: Verma, Shally <Shally.Verma@cavium.com>; Stephen Hemminger
> <stephen@networkplumber.org>
> Cc: dev@dpdk.org; akhil.goyal@nxp.com; Jozwiak, TomaszX
> <tomaszx.jozwiak@intel.com>; Gupta, Ashish <Ashish.Gupta@cavium.com>;
> Daly, Lee <lee.daly@intel.com>; Luse, Paul E <paul.e.luse@intel.com>; Trahe,
> Fiona <fiona.trahe@intel.com>
> Subject: Re: [dpdk-dev] [PATCH] compressdev: add feature flag to specify
> where processing is done
> 
> Hi Shally,
> 
> > -----Original Message-----
> > From: Verma, Shally [mailto:Shally.Verma@cavium.com]
> > Sent: Tuesday, December 18, 2018 10:48 PM
> > To: Trahe, Fiona <fiona.trahe@intel.com>; Stephen Hemminger
> > <stephen@networkplumber.org>
> > Cc: dev@dpdk.org; akhil.goyal@nxp.com; Jozwiak, TomaszX
> > <tomaszx.jozwiak@intel.com>; Gupta, Ashish
> <Ashish.Gupta@cavium.com>;
> > Daly, Lee <lee.daly@intel.com>; Luse, Paul E <paul.e.luse@intel.com>
> > Subject: RE: [dpdk-dev] [PATCH] compressdev: add feature flag to
> > specify where processing is done
> >
> >
> >
> > >-----Original Message-----
> > >From: Trahe, Fiona <fiona.trahe@intel.com>
> > >Sent: 18 December 2018 20:13
> > >To: Stephen Hemminger <stephen@networkplumber.org>
> > >Cc: dev@dpdk.org; akhil.goyal@nxp.com; Jozwiak, TomaszX
> > ><tomaszx.jozwiak@intel.com>; Verma,
> > Shally
> > ><Shally.Verma@cavium.com>; Gupta, Ashish
> <Ashish.Gupta@cavium.com>;
> > >Daly, Lee
> > <lee.daly@intel.com>; Luse, Paul E
> > ><paul.e.luse@intel.com>; Trahe, Fiona <fiona.trahe@intel.com>
> > >Subject: RE: [dpdk-dev] [PATCH] compressdev: add feature flag to
> > >specify where processing is done
> > >
> > >External Email
> > >
> > >Hi Stephen
> > >
> > >//snip//
> > >> > > Subject: Re: [dpdk-dev] [PATCH] compressdev: add feature flag
> > >> > > to specify where processing is
> > done
> > >> > >
> > >> > > On Tue, 20 Nov 2018 01:39:48 +0000 Fiona Trahe
> > >> > > <fiona.trahe@intel.com> wrote:
> > >> > >
> > >> > > > A new device feature flag,
> > >> > > > RTE_COMPDEV_FF_SW_OP_DONE_IN_DEQUEUE
> > >> > > > is added. A PMD which processes operations using a software
> > >> > > > acceleration engine should set this if the bulk of the
> > >> > > > processing is done during the dequeue. It should leave it
> > >> > > > cleared if the bulk of the processing is done during the
> > >> > > > enqueue (default).
> > >> > > > An application may find this useful for tuning.
> > >> > > >
> > >> > > > Signed-off-by: Fiona Trahe <fiona.trahe@intel.com>
> > >> > >
> > >> > > What application? or is this "if we build it they will come?"
> > >> > [Fiona] Our storage team asked for this, so not quite.
> > >> > Seems like it might by generically useful, so a bit of the latter
> > >> > too :) Would you prefer I removed that line?
> > >>
> > >> Hopefully, there would be one or more open source projects using the
> API.
> > >> I just did a survey of DPDK an 1/3 of it is never used by any open
> > >> source project.  Hate to see more dead code and special cases created.
> > >>
> > >> At least, some example code in examples would help. Something like
> > >> a simple in memory compressed storage server using a network API
> > >> (SMB?/SSH?/FTP?)
> > >[Fiona] There is no compressdev sample app yet.
> > >However I've double-checked with the SPDK team, they're currently
> > >integrating compressdev and intend to push a patch to SPDK - a storage
> open-source project - using this flag.
> > [Shally] Am seeing some of our HW based PMD also leveraging this
> > choice. So I would say to make it generic feature flag instead of SW specific.
>  [Fiona] I can do but would like to understand this better first.
> My understanding of HW offload is that the enqueue is just packaging up
> the op and sending to the HW.
> And the dequeue is just collecting the result from the HW and passing back
> to the op.
> The work is done by the HW accelerator, in between those 2 API calls, not
> using any CPU cycles.
> So what would it mean for HW to set OP_DONE_IN_DEQUEUE?

Any comments on this? I agree with Fiona that this flag makes sense on SW only,
but it seems that you have another use case.

Thanks,
Pablo

> 
> > Thanks
> > Shally