Re: [Lse-tech] Re: [PATCH] New dcache / inode hash tuning patch

[Andi Kleen]

On Fri, Feb 28, 2003 at 02:27:27AM -0800, Paul Menage wrote:
> >But for lookup walking even one cache line - the one containing d_hash -
> >should be needed. Unless d_hash is unlucky enough to cross a cache
> >line for its two members ... but I doubt that.
> 
> No, but on a 32-byte cache line system, d_parent, d_hash and d_name are
> all on different cache lines, and they're used when checking each entry.

... and dcache RCU checks d_bucket and d_move_count too in the hash 
walking loop.

> On 64-byte systems, d_parent and d_hash will be on the same line, but
> d_name is still on a separate line and d_name.hash gets checked before
> d_parent. So bringing these three fields on to the same cacheline
> would theoretically be a win.

Ok you're right. Optimizing the layout a bit would be probably a good 
idea. I won't include it in the hash patchkit for now to not do too
many things with the same patch.

-Andi