Re: [PATCH] New operation for kref to help avoid locks

[Corey Minyard]

Arjan van de Ven wrote:

> On Tue, 2005-03-01 at 12:15 -0800, Greg KH wrote:
>  
>
> > On Sat, Feb 26, 2005 at 04:23:04PM -0600, Corey Minyard wrote:
> >    
> >
> > > Add a routine to kref that allows the kref_put() routine to be
> > > unserialized even when the get routine attempts to kref_get()
> > > an object without first holding a valid reference to it.  This is
> > > useful in situations where this happens multiple times without
> > > freeing the object, as it will avoid having to do a lock/semaphore
> > > except on the final kref_put().
> > >
> > > This also adds some kref documentation to the Documentation
> > > directory.
> > >      
> > I like the first part of the documentation, that's nice.
> >
> > But I don't like the new kref_get_with_check() function that you
> > implemented.  If you look in the -mm tree, kref_put() now returns if
> > this was the last put on the reference count or not, to help with lists
> > of objects with a kref in it.
> >
> > Perhaps you can use that to implement what you need instead?
> >    
Yes, that helps a lot.  I had actually already implemented something 
like that :).  But that's a different thing than avoiding the lock.

It's just that with the I2C stuff, you may be calling kref_put() 20-30 
times for a single operation.  That's a lot of lock/unlock operations.  
But it is wierd, so I understand.  Thanks.

> note that I'm not convinced the "lockless" implementation actually is
> faster. It still uses an atomic variable, which is just as expensive as
> taking a lock normally...
>  
Just doing an atomic operation is not faster than doing a lock, an 
atomic operation, then an unlock?  Am I missing something?

-Corey
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/