On Sat, 5 Sep 2015, Jesper Dangaard Brouer wrote:

The double_cmpxchg without lock prefix still cost 9 cycles, which is
very fast but still a cost (add approx 19 cycles for a lock prefix).

It is slower than local_irq_disable + local_irq_enable that only cost
7 cycles, which the bulking call uses.  (That is the reason bulk calls
with 1 object can almost compete with fastpath).

Hmmm... Guess we need to come up with distinct version of kmalloc() for
irq and non irq contexts to take advantage of that . Most at non irq
context anyways.