On Mon, 2008-08-25 at 10:46 -0500, Christoph Lameter wrote:
quoted text
> Peter Zijlstra wrote:
> >
> > If we combine these two cases, and flip the counter as soon as we've
> > enqueued one callback, unless we're already waiting for a grace period
> > to end - which gives us a longer window to collect callbacks.
> > 
> > And then the rcu_read_unlock() can do:
> > 
> >   if (dec_and_zero(my_counter) && my_index == dying)
> >     raise_softirq(RCU)
> > 
> > to fire off the callback stuff.
> > 
> > /me ponders - there must be something wrong with that...
> > 
> > Aaah, yes, the dec_and_zero is non trivial due to the fact that its a
> > distributed counter. Bugger..
> 
> Then lets make it per cpu. If we get the cpu ops in then dec_and_zero would be
> very cheap.

Hmm, perhaps that might work for classic RCU, as that disables
preemption and thus the counters should always be balanced.

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