On Sun, 2008-09-07 at 04:00 -0700, Andrew Morton wrote:
That might actually be a worthwhile idea, but it will not make
get_online_cpus() atomic. The whole point of get_online_cpus() is to
serialize against actual hotplug operations, so it will have to sleep at
some point.
Now, turning cpu_hotplug.refcount into an atomic_t might be worthwhile
because it will reduce the amount of atomic operations in its fastpath
from 2 to 1.
You'd have to make recount==1 the stable situation and use
atomic_inc_unless() and atomic_dec_and_test() in get_online_cpus() and
put_online_cpus() resp. that way !refcount can signify a hotplug
operation and we'd fall back into the slow paths.
--
