From mboxrd@z Thu Jan  1 00:00:00 1970
From: Olivier MATZ <olivier.matz@6wind.com>
Subject: Re: [PATCH v2] mempool: replace c memcpy code semantics
 with optimized rte_memcpy
Date: Tue, 31 May 2016 23:05:30 +0200
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To: Jerin Jacob <jerin.jacob@caviumnetworks.com>
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Hi Jerin,

>>>  	/* Add elements back into the cache */
>>> -	for (index = 0; index < n; ++index, obj_table++)
>>> -		cache_objs[index] = *obj_table;
>>> +	rte_memcpy(&cache_objs[0], obj_table, sizeof(void *) * n);
>>>  
>>>  	cache->len += n;
>>>  
>>>
>>
>> I also checked in the get_bulk() function, which looks like that:
>>
>> 	/* Now fill in the response ... */
>> 	for (index = 0, len = cache->len - 1;
>> 			index < n;
>> 			++index, len--, obj_table++)
>> 		*obj_table = cache_objs[len];
>>
>> I think we could replace it by something like:
>>
>> 	rte_memcpy(obj_table, &cache_objs[len - n], sizeof(void *) * n);
>>
>> The only difference is that it won't reverse the pointers in the
>> table, but I don't see any problem with that.
>>
>> What do you think?
> 
> In true sense, it will _not_ be LIFO. Not sure about cache usage implications
> on the specific use cases.

Today, the objects pointers are reversed only in the get(). It means
that this code:

	rte_mempool_get_bulk(mp, table, 4);
	for (i = 0; i < 4; i++)
		printf("obj = %p\n", t[i]);
	rte_mempool_put_bulk(mp, table, 4);


	printf("-----\n");
	rte_mempool_get_bulk(mp, table, 4);
	for (i = 0; i < 4; i++)
		printf("obj = %p\n", t[i]);
	rte_mempool_put_bulk(mp, table, 4);

prints:

	addr1
	addr2
	addr3
	addr4
	-----
	addr4
	addr3
	addr2
	addr1

Which is quite strange.

I don't think it would be an issue to replace the loop by a
rte_memcpy(), it may increase the copy speed and it will be
more coherent with the put().


Olivier