On Tue, 8 Sep 2015 12:32:40 -0500 (CDT)
Christoph Lameter [off-list ref] wrote:

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

quoted

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.

I agree, it would be an easy win.  Do notice this will have the most
impact for the slAb allocator.

I estimate alloc + free cost would save:
 * slAb would save approx 60 cycles
 * slUb would save approx  4 cycles

We might consider keeping the slUb approach as it would be more
friendly for RT with less IRQ disabling.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>