[dpdk-dev] [RFC v2 01/17] mempool: fix phys contig check if populate default skipped

[Andrew Rybchenko]

On 02/01/2018 01:33 PM, santosh wrote:
> On Thursday 01 February 2018 03:44 PM, Olivier Matz wrote:
>> On Thu, Feb 01, 2018 at 01:00:12PM +0300, Andrew Rybchenko wrote:
>>> On 02/01/2018 12:30 PM, santosh wrote:
>>>> On Thursday 01 February 2018 02:48 PM, Andrew Rybchenko wrote:
>>>>> On 02/01/2018 12:09 PM, santosh wrote:
>>>>>> On Thursday 01 February 2018 12:24 PM, Andrew Rybchenko wrote:
>>>>>>> On 02/01/2018 08:05 AM, santosh wrote:
>>>>>>>> On Wednesday 31 January 2018 10:15 PM, Olivier Matz wrote:
>>>>>>>>> On Tue, Jan 23, 2018 at 01:15:56PM +0000, Andrew Rybchenko wrote:
>>>>>>>>>> There is not specified dependency between rte_mempool_populate_default()
>>>>>>>>>> and rte_mempool_populate_iova(). So, the second should not rely on the
>>>>>>>>>> fact that the first adds capability flags to the mempool flags.
>>>>>>>>>>
>>>>>>>>>> Fixes: 65cf769f5e6a ("mempool: detect physical contiguous objects")
>>>>>>>>>> Cc: stable at dpdk.org
>>>>>>>>>>
>>>>>>>>>> Signed-off-by: Andrew Rybchenko <arybchenko at solarflare.com>
>>>>>>>>> Looks good to me. I agree it's strange that the mp->flags are
>>>>>>>>> updated with capabilities only in rte_mempool_populate_default().
>>>>>>>>> I see that this behavior is removed later in the patchset since the
>>>>>>>>> get_capa() is removed!
>>>>>>>>>
>>>>>>>>> However maybe this single patch could go in 18.02.
>>>>>>>>> +Santosh +Jerin since it's mostly about Octeon.
>>>>>>>> rte_mempool_xmem_size should return correct size if MEMPOOL_F_CAPA_BLK_ALIGNED_OBJECTS flag
>>>>>>>> is set in 'mp->flags'. Thats why _ops_get_capabilities() called in _populate_default() but not
>>>>>>>> at _populate_iova().
>>>>>>>> I think, this 'alone' patch may break octeontx mempool.
>>>>>>> The patch does not touch rte_mempool_populate_default().
>>>>>>> _ops_get_capabilities() is still called there before
>>>>>>> rte_mempool_xmem_size(). The theoretical problem which
>>>>>>> the patch tries to fix is the case when
>>>>>>> rte_mempool_populate_default() is not called at all. I.e. application
>>>>>>> calls _ops_get_capabilities() to get flags, then, together with
>>>>>>> mp->flags, calls rte_mempool_xmem_size() directly, allocates
>>>>>>> calculated amount of memory and calls _populate_iova().
>>>>>>>
>>>>>> In that case, Application does like below:
>>>>>>
>>>>>>       /* Get mempool capabilities */
>>>>>>       mp_flags = 0;
>>>>>>       ret = rte_mempool_ops_get_capabilities(mp, &mp_flags);
>>>>>>       if ((ret < 0) && (ret != -ENOTSUP))
>>>>>>           return ret;
>>>>>>
>>>>>>       /* update mempool capabilities */
>>>>>>       mp->flags |= mp_flags;
>>>>> Above line is not mandatory. "mp->flags | mp_flags" could be simply
>>>>> passed to  rte_mempool_xmem_size() below.
>>>>>
>>>> That depends and again upto application requirement, if app further down
>>>> wants to refer mp->flags for _align/_contig then better update to mp->flags.
>>>>
>>>> But that wasn't the point of discussion, I'm trying to understand that
>>>> w/o this patch, whats could be the application level problem?
>>> The problem that it is fragile. If application does not use
>>> rte_mempool_populate_default() it has to care about addition
>>> of mempool capability flags into mempool flags. If it is not done,
>>> rte_mempool_populate_iova/virt/iova_tab() functions will work
>>> incorrectly since F_CAPA_PHYS_CONTIG and
>>> F_CAPA_BLK_ALIGNED_OBJECTS are missing.
>>>
>>> The idea of the patch is to make it a bit more robust. I have no
>>> idea how it can break something. If capability flags are already
>>> there - no problem. If no, just make sure that we locally have them.
>> The example given by Santosh will work, but it is *not* the role of the
>> application to update the mempool flags. And nothing says that it is mandatory
>> to call rte_mempool_ops_get_capabilities() before the populate functions.
>>
>> For instance, in testpmd it calls rte_mempool_populate_anon() when using
>> anonymous memory. The capabilities will never be updated in mp->flags.
> Valid case and I agree with your example and explanation.
> With nits change:
> mp->flags |= mp_capa_flags;
>
> Acked-by: Santosh Shukla <santosh.shukla at caviumnetworks.com>

I'll submit the patch separately with this minor change. Thanks.