Read Copy Update

[Doug Rabson]

On Tuesday 16 March 2004 03:17, Bosko Milekic wrote:
> On Thu, Feb 19, 2004 at 09:02:35AM +0000, Doug Rabson wrote:
> > On Wed, 2004-02-18 at 23:26, Jeff Roberson wrote:
> > >
> > > I think that this is a good path to go down, but I really don't
> > > think we're ready yet.  I'd rather see energy spent protecting
> > > code than building more infrastructure.
> >
> > I completely agree. I was just musing about this as a future
> > addition to the locking toolbox. Its certainly not worth trying
> > before enough of the kernel is outside the giant lock to make it
> > worthwhile.
>
>   As Jeff said and you agree, it is probably too early for this now.
>   Also, I've looked at the paper you quote before SCO's announcement
>   (which by the way I had no idea about until now), and I think we'll
>   eventually do just as well in the common case without going to the
>   RCU model at all.

Its a pretty neat idea though. I like the sound of being able to e.g. 
read from the namecache without needing to take an expensive lock. With 
the way 5-CURRENT works, we would probably still need to suppress 
context switching which is expensive on intel processors in the current 
implementation. I guess that could be fixed using some kind of lazy-cli 
scheme.

The main barrier here (apart from the need to push Giant down in more 
places and stabilise the existing implementation) is IBM's patent. The 
SCO IP claim (bogus as it is) only covers Sequent's original 
implementation.