Re: [PATCH] netfilter: use per-CPU r**ursive lock {XV}

Peter Zijlstra
2009-04-28T07:42:10Z

On Mon, 2009-04-27 at 16:32 -0700, Linus Torvalds wrote:
>
> On Mon, 27 Apr 2009, Linus Torvalds wrote:
> >
> > I left the commentary about "readers" and "writers", because in many
> > ways it's correct, and what the code actually does is very much to
> > emulate a reader-writer lock. I put quotes around the uses in the
> > comments to high-light that it largely _acts_ as a reader-writer lock.
>
> Btw, I think it was Paul who pointed out that technically it's probably
> better to call them "local" and "global" lockers instead of "readers" and
> "writers".

exclusive vs non-exclusive is what the literature would call them in
most cases I think.

> That also probably clarifies the rules on when you use one over the other
> (ie reading off all the statistics is a "global" operation, as is
> obviously replacing the tables).
>
> Of course, "readers" and "writers" is something most Linux lock people are
> more used to. Or "brlock" for the old-timers, but that involves a heavy
> dose of bad taste. The new use is much nicer, especially since it never
> takes the global lock on _all_ cpu's (which was really a killer in so
> many ways).
>
> Linus