Re: [rfc][patch 1/3] slub: fix small HWCACHE_ALIGN alignment

Nick Piggin
2008-03-07T03:10:57Z

On Thu, Mar 06, 2008 at 06:54:19PM -0800, Christoph Lameter wrote:
> > It doesn't say start of cache line. It says align them *on* cachelines.
> > 2 32 byte objects on a 64 byte cacheline are aligned on the cacheline.
> > 2.67 24 bytes objects on a 64 byte cacheline are not aligned on the
> > cacheline.
>
> 2 32 byte objects means only one is aligned on a cache line.
>
> Certainly cacheline contention is reduced and performance potentially
> increased if there are less objects in a cacheline.
>
> The same argument can be made of aligning 8 byte objects on 32 byte
> boundaries. Instead of 8 objects per cacheline you only have two. Why 8?
>
> Isnt all of this a bit arbitrary and contrary to the intend of avoiding
> cacheline contention?

No, it *is not about avoiding cacheline contention*. As such, the rest
of what you wrote below about smp_align etc is rubbish.

Can you actually read what I posted?