Re: speed difference between using hard-linked and modular drives?

David S. Miller
2001-11-09T07:17:00Z

From: Andi Kleen <ak@suse.de>
Date: Fri, 9 Nov 2001 07:39:46 +0100

I'm assuming that walking on average 5-10 pages on a lookup is not
too big a deal, especially when you use prefetch for the list walk.

Oh no, not this again...

It _IS_ a big deal. Fetching _ONE_ hash chain cache line
is always going to be cheaper than fetching _FIVE_ to _TEN_
page struct cache lines while walking the list.

Even if prefetch would kill all of this overhead (sorry, it won't), it
is _DUMB_ and _STUPID_ to bring those _FIVE_ to _TEN_ cache lines into
the processor just to lookup _ONE_ page.

Franks a lot,
David S. Miller
davem@redhat.com