Read Copy Update

[Bosko Milekic]

On Tue, Mar 16, 2004 at 09:14:51AM +0000, Doug Rabson wrote:
> 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.

  Should be really easy to fix in the common case without having to get
  really fancy (e.g., just interlock against ourselves on a private
  per-thread flag) to merely delay cli until the first interrupt.  We
  shouldn't need to mask out per CPU or anything fancy like that.

> 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.

  Yeah, that sucks.

-- 
Bosko Milekic  *  bmilekic at technokratis.com  *  bmilekic at FreeBSD.org
TECHNOkRATIS Consulting Services  *  http://www.technokratis.com/

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 he already knows."  -- Epictetus (c.a.d. 55-c135)