Re: [dpdk-dev] lib: include rte_memory.h for __rte_cache_aligned

[Olivier MATZ <olivier.matz@6wind.com>]

Hi Neil,

On 12/08/2014 04:04 PM, Neil Horman wrote:
> On Fri, Nov 07, 2014 at 09:28:09AM -0800, Jia Yu wrote:
>> Include rte_memory.h for lib files that use __rte_cache_aligned
>> attribute.
>>
>> Signed-off-by: Jia Yu <jyu@vmware.com>
>>
> Why?  I presume there was a build break or something.  Please repost with a
> changelog that details what this patch is for.
> Neil

I don't know if Yu's issue was the same, but I had a very "fun" issue
with __rte_cache_aligned in my application. Consider the following code:

	struct per_core_foo {
		...
	} __rte_cache_aligned;

	struct global_foo {
		struct per_core_foo foo[RTE_MAX_CORE];
	};

If __rte_cache_aligned is not defined (rte_memory.h is not included),
the code compiles but the structure is not aligned... it defines the
structure and creates a global variable called __rte_cache_aligned.
And this can lead to really bad things if this code is in a .h that
is included by files that may or may not include rte_memory.h

I have no idea about how we could prevent this issue, except using
__attribute__((aligned(CACHE_LINE))) instead of __rte_cache_aligned.

Anyway this could probably explain the willing to include rte_memory.h
everywhere.

Regards,
Olivier