lkml.org 
[lkml]   [2010]   [Nov]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [thiscpuops upgrade 08/10] percpu: generic this_cpu_cmpxchg() and this_cpu_cmpxchg_double support
From
Date
Le vendredi 26 novembre 2010 à 18:07 +0100, Tejun Heo a écrit :
> On 11/26/2010 06:01 PM, Eric Dumazet wrote:
> >> What I'm afraid of is generic code switching to use it in very hot
> >> paths when a lot of archs can't actually do it leading to performance
> >> regressions. Is this something which is available on most archs?
> >>
> >
> > I would say cmpxchg() has the same problem, some arches dont have a
> > native instruction, yet we use it in some paths.
>
> Yeah, well, there's difference between some not having it and only
> x86_64 having it. cmpxchg was already rather well received when it
> was added even though it wasn't available on all archs. I'm not
> against it but think we should use some caution here and think about
> the impact of unoptimized cases which can be pretty common (preemption
> toggling isn't too expensive but irq toggling can be quite).
>


x86_32 has it too

x86_64 uses cmpxchg16b, while x86_32 uses cmpxhg8b


And I guess it will be used in contexts we had to disable irqs, so it
will be faster on x86, and same cost on other arches.



--
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/

\
 
 \ /
  Last update: 2010-11-26 18:19    [W:0.081 / U:0.492 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site