HI Fiona

So I understand we're moving away from mbufs because of its size limitation 
(64k) and cacheline overhead and their more suitability to n/w applications. 
Given that, I understand benefit of having another structure to input data but 
then what is proposal for ipcomp like application where mbuf usage may be a 
better option? Should we keep support for both (mbuf and this structure) so 
that apps can use appropriate data structure depending on their requirement.

Further comments, on github.


>-----Original Message-----
>From: Trahe, Fiona [mailto:fiona.tr...@intel.com]
>Sent: 12 March 2018 21:31
>To: Ahmed Mansour <ahmed.mans...@nxp.com>; Verma, Shally 
><shally.ve...@cavium.com>; dev@dpdk.org
>Cc: De Lara Guarch, Pablo <pablo.de.lara.gua...@intel.com>; Athreya, Narayana 
>Prasad <narayanaprasad.athr...@cavium.com>;
>Gupta, Ashish <ashish.gu...@cavium.com>; Sahu, Sunila 
><sunila.s...@cavium.com>; Challa, Mahipal
><mahipal.cha...@cavium.com>; Jain, Deepak K <deepak.k.j...@intel.com>; Hemant 
>Agrawal <hemant.agra...@nxp.com>; Roy
>Pledge <roy.ple...@nxp.com>; Youri Querry <youri.querr...@nxp.com>; 
>fiona.tr...@gmail.com; Daly, Lee <lee.d...@intel.com>;
>Jozwiak, TomaszX <tomaszx.jozw...@intel.com>
>Subject: RE: [dpdk-dev] [PATCH] compressdev: implement API - mbuf alternative
>Hi Shally, Ahmed, and anyone else interested in compressdev,
>I mentioned last week that we've been exploring using something other than 
>mbufs to pass src/dst buffers to compressdev PMDs.
> - mbuf data is limited to 64k-1 in each segment of a chained mbuf. Data for 
> compression
>    can be greater and it would add cycles to have to break up into smaller 
> segments.
> - data may originate in mbufs, but is more likely, particularly for storage 
> use-cases,  to
>    originate in other data structures.
> - There's a 2 cache-line overhead for every segment in a chain, most of this 
> data
>    is network-related, not needed by compressdev
>So moving to a custom structure would minimise memory overhead, remove 
>restriction on 64k-1 size and give more flexibility if
>compressdev ever needs any comp-specific meta-data.
>We've come up with a compressdev-specific structure using the struct iovec 
>from sys/uio.h, which is commonly used by storage
>applications. This would replace the src and dest mbufs in the  op.
>I'll not include the code here - Pablo will push that to github shortly and 
>we'd appreciate review comments there.
>Just posting on the mailing list to give a heads-up and ensure this reaches a 
>wider audience than may see it on github.
>Note : We also considered having no data structures in the op, instead the 
>would supply a callback which the PMD would use to retrieve meta-data (virt 
>address, iova, length)
>for each next segment as needed. While this is quite flexible and allow the 
>to keep its data in its native structures, it's likely to cost more cycles.
>So we're not proposing this at the moment, but hope to benchmark it later 
>while the API is still experimental.
>General feedback on direction is welcome here on the mailing list.
>For feedback on the details of implementation we would appreciate comments on 

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