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To: Shreyansh Jain <shreyansh.jain@nxp.com>
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From: "Burakov, Anatoly" <anatoly.burakov@intel.com>
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Date: Thu, 11 Oct 2018 10:03:35 +0100
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Subject: Re: [dpdk-dev] [PATCH 3/5] common/dpaax: add library for PA VA
translation table
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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