[dpdk-dev] [PATCH v4 6/7] mempool: introduce block size align flag

[santosh]

On Monday 04 September 2017 09:50 PM, Olivier MATZ wrote:
> On Tue, Aug 15, 2017 at 11:37:42AM +0530, Santosh Shukla wrote:
>> Some mempool hw like octeontx/fpa block, demands block size
>> (/total_elem_sz) aligned object start address.
>>
>> Introducing an MEMPOOL_F_POOL_BLK_SZ_ALIGNED flag.
>> If this flag is set:
>> - Align object start address to a multiple of total_elt_sz.
> Please specify if it's virtual or physical address.

virtual address. Yes will mention in v5. Thanks.

> What do you think about MEMPOOL_F_BLK_ALIGNED_OBJECTS instead?
>
> I don't really like BLK because the word "block" is not used anywhere
> else in the mempool code. But I cannot find any good replacement for
> it. If you have another idea, please suggest.
>
Ok with renaming to MEMPOOL_F_BLK_ALIGNED_OBJECTS

>> - Allocate one additional object. Additional object is needed to make
>>   sure that requested 'n' object gets correctly populated. Example:
>>
>> - Let's say that we get 'x' size of memory chunk from memzone.
>> - And application has requested 'n' object from mempool.
>> - Ideally, we start using objects at start address 0 to...(x-block_sz)
>>   for n obj.
>> - Not necessarily first object address i.e. 0 is aligned to block_sz.
>> - So we derive 'offset' value for block_sz alignment purpose i.e..'off'.
>> - That 'off' makes sure that start address of object is blk_sz
>>   aligned.
>> - Calculating 'off' may end up sacrificing first block_sz area of
>>   memzone area x. So total number of the object which can fit in the
>>   pool area is n-1, Which is incorrect behavior.
>>
>> Therefore we request one additional object (/block_sz area) from memzone
>> when F_BLK_SZ_ALIGNED flag is set.
>>
>> Signed-off-by: Santosh Shukla <santosh.shukla at caviumnetworks.com>
>> Signed-off-by: Jerin Jacob <jerin.jacob at caviumnetworks.com>
>> ---
>>  lib/librte_mempool/rte_mempool.c | 16 +++++++++++++---
>>  lib/librte_mempool/rte_mempool.h |  1 +
>>  2 files changed, 14 insertions(+), 3 deletions(-)
>>
>> diff --git a/lib/librte_mempool/rte_mempool.c b/lib/librte_mempool/rte_mempool.c
>> index 19e5e6ddf..7610f0d1f 100644
>> --- a/lib/librte_mempool/rte_mempool.c
>> +++ b/lib/librte_mempool/rte_mempool.c
>> @@ -239,10 +239,14 @@ rte_mempool_calc_obj_size(uint32_t elt_size, uint32_t flags,
>>   */
>>  size_t
>>  rte_mempool_xmem_size(uint32_t elt_num, size_t total_elt_sz, uint32_t pg_shift,
>> -		      __rte_unused const struct rte_mempool *mp)
>> +		      const struct rte_mempool *mp)
>>  {
>>  	size_t obj_per_page, pg_num, pg_sz;
>>  
>> +	if (mp && mp->flags & MEMPOOL_F_POOL_BLK_SZ_ALIGNED)
>> +		/* alignment need one additional object */
>> +		elt_num += 1;
>> +
>>  	if (total_elt_sz == 0)
>>  		return 0;
> I'm wondering if it's correct if the mempool area is not contiguous.
>
> For instance:
>  page size = 4096
>  object size = 1900
>  elt_num = 10
>
> With your calculation, you will request (11+2-1)/2 = 6 pages.
> But actually you may need 10 pages (max), since the number of object per
> page matching the alignement constraint is 1, not 2.
>
In our case, we set PMD flag MEMPOOL_F_CAPA_PHYS_CONTIG to detect contiguity,
would fail at pool creation time, as HW don't support.