Re: SMP/cc Cluster description

[Davide Libenzi]

On Thu, 6 Dec 2001, Rik van Riel wrote:

> On Wed, 5 Dec 2001, Davide Libenzi wrote:
> > On Thu, 6 Dec 2001, Rusty Russell wrote:
> >
> > > I'd love to say that I can solve this with RCU, but it's vastly non-trivial
> > > and I haven't got code, so I'm not going to say that. 8)
> >
> > Lockless algos could help if we're able to have "good" quiescent point
> > inside the kernel. Or better have a good quiescent infrastructure to
> > have lockless code to plug in.
>
> Machines get dragged down by _uncontended_ locks, simply
> due to cache line ping-pong effects.

Rik, i think you're confused about lockless algos.
It's not an rwlock where the reader has to dirty a cacheline in any case,
the reader simply does _not_ write any cache line accessing the
list/hash/tree or whatever you use.
These algo uses barries and all changes are done when the system walk
through a quiescent state by flushing a list-of-changes.
Drawback, you've to be able to tollerate stale data.

- Davide