Re: [RFC] Refcounting of objects part of a lockfree collection

[Greg KH <greg@kroah.com>]

On Wed, Jul 14, 2004 at 02:27:58PM +0530, Ravikiran G Thirumalai wrote:
> On Wed, Jul 14, 2004 at 12:07:00AM -0700, Greg KH wrote:
> > On Wed, Jul 14, 2004 at 10:23:50AM +0530, Ravikiran G Thirumalai wrote:
> > > 
> > > The attatched patch provides infrastructure for refcounting of objects
> > > in a rcu protected collection.
> > 
> > This is really close to the kref implementation.  Why not just use that
> > instead?
> 
> Close, but not the same.  I just had a quick look at krefs.
> Actually, this refrerence count infrastructure I am proposing is not for 
> traditional refcounting.

But you are advertising it as such by calling it a refcount_t and
putting it in a file called refcount.h.

> > Oh, and I think you need to use atomic_set() instead of initializing the
> > atomic_t by hand.
> 
> I have used atomic_set for the case where arch has cmpxchg.  But for 
> arches lacking cmpxchg, I need to use hashed spinlocks to implement 
> the ref_count_get_rcu.
> No point in having more atomic operations when I hold spinlocks.  Admittedly,
> might be a bit yucky to assume atomic_t internals, but it is just one header
> file :) <ducks>

I still think you need to fix this, manipulating atomic_t variables by
hand is not always guaranteed to work on all arches, from what I
remember.

And what arches do not support cmpxchg?  How does this change affect the
performance of them?

thanks,

greg k-h