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

[Thomas Monjalon <thomas.monjalon@6wind.com>]

2014-12-09 10:22, Neil Horman:
> On Tue, Dec 09, 2014 at 09:53:18AM +0100, Olivier MATZ wrote:
> > 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
> 
> So, that is a great explination, and would be good to have in the changelog.

Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>

Applied with Olivier's explanation.

Thanks
-- 
Thomas