Re: [PATCH v2] mempool: replace c memcpy code semantics with optimized rte_memcpy

[Olivier MATZ <olivier.matz@6wind.com>]

Hi Jerin,

On 06/01/2016 09:00 AM, Jerin Jacob wrote:
> On Tue, May 31, 2016 at 11:05:30PM +0200, Olivier MATZ wrote:
>> Today, the objects pointers are reversed only in the get(). It means
>> that this code:
>>
>> 	rte_mempool_get_bulk(mp, table, 4);
>> 	for (i = 0; i < 4; i++)
>> 		printf("obj = %p\n", t[i]);
>> 	rte_mempool_put_bulk(mp, table, 4);
>>
>>
>> 	printf("-----\n");
>> 	rte_mempool_get_bulk(mp, table, 4);
>> 	for (i = 0; i < 4; i++)
>> 		printf("obj = %p\n", t[i]);
>> 	rte_mempool_put_bulk(mp, table, 4);
>>
>> prints:
>>
>> 	addr1
>> 	addr2
>> 	addr3
>> 	addr4
>> 	-----
>> 	addr4
>> 	addr3
>> 	addr2
>> 	addr1
>>
>> Which is quite strange.
> 
> IMO, It is the expected LIFO behavior. Right ?
> 
> What is not expected is the following, which is the case after change. Or Am I
> missing something here?
> 
> addr1
> addr2
> addr3
> addr4
> -----
> addr1
> addr2
> addr3
> addr4
> 
>>
>> I don't think it would be an issue to replace the loop by a
>> rte_memcpy(), it may increase the copy speed and it will be
>> more coherent with the put().
>>

I think the LIFO behavior should occur on a per-bulk basis. I mean,
it should behave like in the exemplaes below:

  // pool cache is in state X
  obj1 = mempool_get(mp)
  obj2 = mempool_get(mp)
  mempool_put(mp, obj2)
  mempool_put(mp, obj1)
  // pool cache is back in state X

  // pool cache is in state X
  bulk1 = mempool_get_bulk(mp, 16)
  bulk2 = mempool_get_bulk(mp, 16)
  mempool_put_bulk(mp, bulk2, 16)
  mempool_put_bulk(mp, bulk1, 16)
  // pool cache is back in state X

Note that today it's not the case for bulks, since object addresses
are reversed only in get(), we are not back in the original state.
I don't really see the advantage of this.

Removing the reversing may accelerate the cache in case of bulk get,
I think.

Regards,
Olivier