Re: SMP/cc Cluster description

David S. Miller
2001-12-06T07:57:27Z

From: Davide Libenzi <davidel@xmailserver.org>
Date: Wed, 5 Dec 2001 19:19:19 -0800 (PST)

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.

Lockless algorithms don't get rid of the shared cache lines.

I used to once think that lockless algorithms were the SMP holy-grail,
but this was undone when I realized they had the same fundamental
overhead spinlocks do.

These lockless algorithms, instructions like CAS, DCAS, "infinite
consensus number", it's all crap. You have to seperate out the access
areas amongst different cpus so they don't collide, and none of these
mechanisms do that.

That is, unless some lockless algorithm involving %100 local dirty
state has been invented while I wasn't looking :-)