On Sat, Dec 07, 2002 at 03:29:16PM -0800, Andrew Morton wrote:
> Jeff Garzik wrote:
> >
> > David S. Miller wrote:
> > > Can't the cacheline_aligned attribute be applied to individual
> > > struct members? I remember doing this for thread_struct on
> > > sparc ages ago.
> >
> > Looks like it from the 2.4 processor.h code.
> >
> > Attached is cut #2. Thanks for all the near-instant feedback so far :)
> > Andrew, does the attached still need padding on SMP?
>
> It needs padding _only_ on SMP. ____cacheline_aligned_in_smp.
>
> #define offsetof(t, m) ((int)(&((t *)0)->m))
>
> struct foo {
> int a;
> int b __attribute__((__aligned__(1024)));
> int c;
> } foo;
>
> main()
> {
> printf("%d\n", sizeof(struct foo));
> printf("%d\n", offsetof(struct foo, a));
> printf("%d\n", offsetof(struct foo, b));
> printf("%d\n", offsetof(struct foo, c));
> }
>
> ./a.out
> 2048
> 0
> 1024
> 1028
>
> So your patch will do what you want it to do. You should just tag the
> first member of a group with ____cacheline_aligned_in_smp, and keep an
> eye on things with offsetof().
>
> Not sure why sizeof() returned 2048 though.
The structure contains an __aligned__(1024) item. Think about an array
of 'struct foo' items. They have to be 2048 bytes or you won't align
correctly.
C allows for empty space in structure padding, but not in arrays,
AFAIK.
-- Daniel Jacobowitz MontaVista Software Debian GNU/Linux Developer - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Sat Dec 07 2002 - 22:00:31 EST