On Fri, Aug 04, 2017 at 10:05:55AM +0800, Huang, Ying wrote:
> "Huang, Ying" <ying.hu...@intel.com> writes:
> > Peter Zijlstra <pet...@infradead.org> writes:
> >> +struct __call_single_data {
> >> struct llist_node llist;
> >> smp_call_func_t func;
> >> void *info;
> >> unsigned int flags;
> >> };
> >>
> >> +typedef struct __call_single_data call_single_data_t
> >> + __aligned(sizeof(struct __call_single_data));
> >> +
> >
> > Another requirement of the alignment is that it should be the power of
> > 2. Otherwise, for example, if someone adds a field to struct, so that
> > the size becomes 40 on x86_64. The alignment should be 64 instead of
> > 40.
>
> Thanks Aaron, he reminded me that there is a roundup_pow_of_two(). So
> the typedef could be,
>
> typedef struct __call_single_data call_single_data_t
> __aligned(roundup_pow_of_two(sizeof(struct __call_single_data));
>
Yes, that would take away the requirement to play padding games with the
struct. Then again, maybe its a good thing to have to be explicit about
it.
If you see:
struct __call_single_data {
struct llist_node llist;
smp_call_func_t func;
void *info
int flags;
void *extra_field;
unsigned long __padding[3]; /* make align work */
};
that makes it very clear what is going on. In any case, we can delay
this part because the current structure is a power-of-2 for both ILP32
and LP64. So only the person growing this will have to deal with it ;-)
