Sorry for not commenting earlier, I was traveling and keeping email to
a minimum..
On Wed, Jun 26, 2013 at 10:43 AM, Waiman Long <Waiman.Long@xxxxxx> wrote:
> This patch introduces a new spinlock_refcount.h header file to be
> included by kernel code that want to do a lockless update of reference
> count protected by a spinlock.
So I really like the concept, but the implementation is a mess, and
tries to do too much, while actually achieving too little.
I do not believe you should care about debug spinlocks at all, and
just leave them be. Have a simple fallback code that defaults to
regular counts and spinlocks, and have any debug cases just use that.
But more importantly, I think this needs to be architecture-specific,
and using <linux/spinlock_refcount.h> to try to do some generic 64-bit
cmpxchg() version is a bad bad idea.
We have several architectures coming up that have memory transaction
support, and the "spinlock with refcount" is a perfect candidate for a
transactional memory implementation. So when introducing a new atomic
like this that is very performance-critical and used for some very
core code, I really think architectures would want to make their own
optimized versions.
These things should also not be inlined, I think.
So I think the concept is good, but I think the implementation needs
more thought.
Linus
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
