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To: "Hunt, David" <david.hunt@intel.com>,
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From: Olivier MATZ <olivier.matz@6wind.com>
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Date: Thu, 16 Jun 2016 10:47:03 +0200
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Subject: Re: [dpdk-dev] [PATCH v12 0/3] mempool: add external mempool manager
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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.