Re: Pls apply this spinlock patch to the kernel

[Richard Henderson <rth@twiddle.net>]

On Mon, Oct 29, 2001 at 09:32:52AM -0800, Linus Torvalds wrote:
> On Mon, 29 Oct 2001, Alan Cox wrote:
> > spinlock_t pagecache_lock ____cacheline_aligned_in_smp = SPIN_LOCK_UNLOCKED;
> > cache_line_pad;
> >
> > where cache_line_pad is an asm(".align") - I would assume that is
> > sufficient - Linus ?

The "cache_line_pad" is useless.  The __attribute__((aligned(N)))
is completely sufficient.

> Gcc won't guarantee that it puts different variables adjacently - the
> linker (or even the compiler) can move things around to make them fit
> better. Which is why it would be better to use the separate section trick.

Separate sections are also not needed.  While you can't guarantee
adjacency, the object file *does* record the required alignment 
and that must be honored by the linker.

Now, separate sections do make sense for minimizing accumulated 
padding, but that is a separate issue.


r~