Re: [dpdk-dev] [RFC v2] doc compression API for DPDK

[Ahmed Mansour <ahmed.mansour@nxp.com>]

On 2/14/2018 12:41 AM, Verma, Shally wrote:
> Hi Ahmed
>
>> -----Original Message-----
>> From: Ahmed Mansour [mailto:ahmed.mansour@nxp.com]
>> Sent: 02 February 2018 02:20
>> To: Trahe, Fiona <fiona.trahe@intel.com>; Verma, Shally <Shally.Verma@cavium.com>; dev@dpdk.org
>> Cc: Athreya, Narayana Prasad <NarayanaPrasad.Athreya@cavium.com>; Gupta, Ashish <Ashish.Gupta@cavium.com>; Sahu, Sunila
>> <Sunila.Sahu@cavium.com>; De Lara Guarch, Pablo <pablo.de.lara.guarch@intel.com>; Challa, Mahipal
>> <Mahipal.Challa@cavium.com>; Jain, Deepak K <deepak.k.jain@intel.com>; Hemant Agrawal <hemant.agrawal@nxp.com>; Roy
>> Pledge <roy.pledge@nxp.com>; Youri Querry <youri.querry_1@nxp.com>
>> Subject: Re: [RFC v2] doc compression API for DPDK
>>
>>>>> [Fiona] I propose if BFINAL bit is detected before end of input
>>>>> the decompression should stop. In this case consumed will be < src.length.
>>>>> produced will be < dst buffer size. Do we need an extra STATUS response?
>>>>> STATUS_BFINAL_DETECTED  ?
>>>> [Shally] @fiona, I assume you mean here decompressor stop after processing Final block right?
>>> [Fiona] Yes.
>>>
>>>  And if yes,
>>>> and if it can process that final block successfully/unsuccessfully, then status could simply be
>>>> SUCCESS/FAILED.
>>>> I don't see need of specific return code for this use case. Just to share, in past, we have practically run into
>>>> such cases with boost lib, and decompressor has simply worked this way.
>>> [Fiona] I'm ok with this.
>>>
>>>>> Only thing I don't like this is it can impact on performance, as normally
>>>>> we can just look for STATUS == SUCCESS. Anything else should be an exception.
>>>>> Now the application would have to check for SUCCESS || BFINAL_DETECTED every time.
>>>>> Do you have a suggestion on how we should handle this?
>>>>>
>> [Ahmed] This makes sense. So in all cases the PMD should assume that it
>> should stop as soon as a BFINAL is observed.
>>
>> A question. What happens ins stateful vs stateless modes when
>> decompressing an op that encompasses multiple BFINALs. I assume the
>> caller in that case will use the consumed=x bytes to find out how far in
>> to the input is the end of the first stream and start from the next
>> byte. Is this correct?
> [Shally]  As per my understanding, each op can be tied up to only one stream as we have only one stream pointer per op and one stream can have only one BFINAL (as stream is one complete compressed data) but looks like you're suggesting a case where one op can carry multiple independent streams? and thus multiple BFINAL?! , such as, below here is op pointing to more than one streams
>
>             --------------------------------------------
> op --> |stream1|stream2| |stream3|
>            --------------------------------------------
>
> Could you confirm if I understand your question correct?
[Ahmed] Correct. We found that in some storage applications the user
does not know where exactly the BFINAL is. They rely on zlib software
today. zlib.net software halts at the first BFINAL. Users put multiple
streams in one op and rely on zlib to  stop and inform them of the end
location of the first stream.
>
> Thanks
> Shally
>