[dpdk-dev] [PATCH 1/6] ring: change head and tail to pointer-width size

[Burakov, Anatoly]

On 11-Jan-19 10:58 AM, Bruce Richardson wrote:
> On Fri, Jan 11, 2019 at 10:40:19AM +0000, Burakov, Anatoly wrote:
>> <...>
>>
>>> + * Copyright(c) 2016-2019 Intel Corporation
>>>     */
>>>    /**
>>> @@ -88,7 +88,7 @@ rte_event_ring_enqueue_burst(struct rte_event_ring *r,
>>>    		const struct rte_event *events,
>>>    		unsigned int n, uint16_t *free_space)
>>>    {
>>> -	uint32_t prod_head, prod_next;
>>> +	uintptr_t prod_head, prod_next;
>>
>> I would also question the use of uinptr_t. I think semnatically, size_t is
>> more appropriate.
>>
> Yes, it would, but I believe in this case they want to use the largest size
> of (unsigned)int where there exists an atomic for manipulating 2 of them
> simultaneously. [The largest size is to minimize any chance of an ABA issue
> occuring]. Therefore we need 32-bit values on 32-bit and 64-bit on 64, and
> I suspect the best way to guarantee this is to use pointer-sized values. If
> size_t is guaranteed across all OS's to have the same size as uintptr_t it
> could also be used, though.
> 
> /Bruce
> 

Technically, size_t and uintptr_t are not guaranteed to match. In 
practice, they won't match only on architectures that DPDK doesn't 
intend to run on (such as 16-bit segmented archs, where size_t would be 
16-bit but uinptr_t would be 32-bit).

In all the rest of DPDK code, we use size_t for this kind of thing.

-- 
Thanks,
Anatoly