From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Hunt, David" <david.hunt@intel.com>
Subject: Re: [PATCH v12 0/3] mempool: add external mempool manager
Date: Thu, 16 Jun 2016 09:55:46 +0100
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Cc: dev@dpdk.org, jerin.jacob@caviumnetworks.com, shreyansh.jain@nxp.com
To: Olivier MATZ <olivier.matz@6wind.com>,
 Jan Viktorin <viktorin@rehivetech.com>
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On 16/6/2016 9:47 AM, Olivier MATZ wrote:
>
>
> On 06/16/2016 09:47 AM, Hunt, David wrote:
>>
>>
>> On 15/6/2016 5:40 PM, Olivier MATZ wrote:
>>>
>>>
>>> On 06/15/2016 06:34 PM, Hunt, David wrote:
>>>>
>>>>
>>>> On 15/6/2016 1:03 PM, Olivier MATZ wrote:
>>>>> [...]
>>>>>
>>>>> The opaque pointer would be saved in mempool structure, and used
>>>>> when the mempool is populated (calling mempool_ops_alloc).
>>>>> The type of the structure pointed by the opaque has to be defined
>>>>> (and documented) into each mempool_ops manager.
>>>>>
>>>>>
>>>>> Olivier
>>>>
>>>>
>>>> OK, just to be sure before I post another patchset.....
>>>>
>>>> For the rte_mempool_struct:
>>>>          struct rte_mempool_memhdr_list mem_list; /**< List of memory
>>>> chunks */
>>>> +       void *ops_args;                  /**< optional args for ops
>>>> alloc. */
>>>>
>>>> (at the end of the struct, as it's just on the control path, not to
>>>> affect fast path)
>>>
>>> Hmm, I would put it just after pool_data.
>>>
>>
>> When I move it to just after pool data, the performance of the
>> mempool_perf_autotest drops by 2% on my machine for the local cache 
>> tests.
>> I think I should leave it where I suggested.
>
> I don't really see what you call control path and data path here.
> For me, all the fields in mempool structure are not modified once
> the mempool is initialized.
>
> http://dpdk.org/browse/dpdk/tree/lib/librte_mempool/rte_mempool.h?id=ce94a51ff05c0a4b63177f8a314feb5d19992036#n201 
>
>
> So I don't think we should have more cache misses whether it's
> placed at the beginning or at the end. Maybe I'm missing something...
>
> I still believe it's better to group the 2 fields as they are
> tightly linked together. It could be at the end if you see better
> performance.
>

OK, I'll leave at the end because of the performance hit.

Regards,
David.