Re: [dpdk-dev] [PATCH 3/5] common/dpaax: add library for PA VA translation table

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 09-Oct-18 11:45 AM, Shreyansh Jain wrote:
> On Tuesday 25 September 2018 07:09 PM, Shreyansh Jain wrote:
>> Hello Anatoly,
>>
>> On Tuesday 25 September 2018 06:58 PM, Burakov, Anatoly wrote:
>>> On 25-Sep-18 1:54 PM, Shreyansh Jain wrote:
>>>> A common library, valid for dpaaX drivers, which is used to maintain
>>>> a local copy of PA->VA translations.
>>>>
>>>> In case of physical addressing mode (one of the option for FSLMC, and
>>>> only option for DPAA bus), the addresses of descriptors Rx'd are
>>>> physical. These need to be converted into equivalent VA for rte_mbuf
>>>> and other similar calls.
>>>>
>>>> Using the rte_mem_virt2iova or rte_mem_virt2phy is expensive. This
>>>> library is an attempt to reduce the overall cost associated with
>>>> this translation.
>>>>
>>>> A small table is maintained, containing continuous entries
>>>> representing a continguous physical range. Each of these entries
>>>> stores the equivalent VA, which is fed during mempool creation, or
>>>> memory allocation/deallocation callbacks.
>>>>
> 
> [...]
> 
>>
>>>
>>> Also, a couple of nitpicks below.
>>>
>>>>   cosnfig/common_base                            |   5 +
>>>>   config/common_linuxapp                        |   5 +
>>>>   drivers/common/Makefile                       |   4 +
>>>>   drivers/common/dpaax/Makefile                 |  31 ++
>>>>   drivers/common/dpaax/dpaax_iova_table.c       | 509 
>>>> ++++++++++++++++++
>>>>   drivers/common/dpaax/dpaax_iova_table.h       | 104 ++++
>>>>   drivers/common/dpaax/dpaax_logs.h             |  39 ++
>>>>   drivers/common/dpaax/meson.build              |  12 +
>>>
>>> <snip>
>>>
>>>> +    DPAAX_DEBUG("Add: Found slot at (%"PRIu64")[(%zu)] for 
>>>> vaddr:(%p),"
>>>> +            " phy(%"PRIu64"), len(%zu)", entry[i].start, e_offset,
>>>> +            vaddr, paddr, length);
>>>> +    return 0;
>>>> +}
>>>> +
>>>> +int
>>>> +dpaax_iova_table_del(phys_addr_t paddr, size_t len __rte_unused)
>>>
>>> len is not unused.
>>
>> I will fix this.
>> Actually, this function itself is useless - more for symmetry reason.
>> Callers would be either simply updating the table, or ignoring it 
>> completely. But, yes, this is indeed wrong that I set that unused.
>>
> 
> Actually, I was wrong in my first reply. In case of 
> dpaax_iova_table_del(), len is indeed redundant. This is because the 
> mapping is for a complete page (min of 2MB size), even if the request is 
> for lesser length. So, removal of a single entry (of fixed size) would 
> be done.
> 
> In fact, while on this, I think deleting a PA->VA entry itself is 
> incorrect (not just useless). A single entry (~2MB equivalent) can 
> represent multiple users (working on a rte_malloc'd area, for example). 
> So, effectively, its always an update - not an add or del.

I'm not sure what you mean here. If you got a mem event about memory 
area being freed, it's guaranteed to *not* have any users - neither 
malloc, nor any other memory. And len is always page-aligned.

> 
> I will send updated series with this change.
> 
> [...]
> 
> 


-- 
Thanks,
Anatoly