From mboxrd@z Thu Jan  1 00:00:00 1970
From: Olivier Matz <olivier.matz@6wind.com>
Subject: Re: [PATCH 26/36] mempool: introduce a function to
 create an empty mempool
Date: Fri, 15 Apr 2016 09:42:32 +0200
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Cc: "Richardson, Bruce" <bruce.richardson@intel.com>,
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To: "Wiles, Keith" <keith.wiles@intel.com>, "dev@dpdk.org" <dev@dpdk.org>
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On 04/14/2016 05:57 PM, Wiles, Keith wrote:
>> Introduce a new function rte_mempool_create_empty()
>> that allocates a mempool that is not populated.
>>
>> The functions rte_mempool_create() and rte_mempool_xmem_create()
>> now make use of it, making their code much easier to read.
>> Currently, they are the only users of rte_mempool_create_empty()
>> but the function will be made public in next commits.
>>
>> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
>> +/* create an empty mempool */
>> +static struct rte_mempool *
>> +rte_mempool_create_empty(const char *name, unsigned n, unsigned elt_size,
>> +	unsigned cache_size, unsigned private_data_size,
>> +	int socket_id, unsigned flags)
>> {
> 
> When two processes need to use the same mempool, do we have a race condition with one doing a rte_mempool_create_empty() and the other process tries to use it when it finds that mempool before being fully initialized by the first process?
> 

I'm not an expert of the dpdk multiprocess model. But I would
say that there are a lot of possible race conditions like this
(ex: a port is created but not started), and I assume that
applications doing multiprocess have their synchronization.

If we really want a solution in mempool, we could:

- remove the TAILQ_INSERT_TAIL() from rte_mempool_create()
- create a new function rte_mempool_share() that adds the
  mempool in the tailq for multiprocess. This function would
  be called at the end of rte_mempool_create(), or by the
  user if using rte_mempool_create_empty().

I may be mistaking but I don't feel it's really required. Any
comment from a multiprocess expert is welcome though.


Regards,
Olivier