lkml.org 
[lkml]   [2008]   [Aug]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/2] smp_call_function: use rwlocks on queues rather than rcu
On Fri, Aug 22, 2008 at 11:35:46AM -0700, Jeremy Fitzhardinge wrote:
> Andi Kleen wrote:
> > Right now my impression is that it is not well understood why
> > the kmalloc makes the IPI that much slower. In theory a kmalloc
> > shouldn't be all that slow, it's essentially just a
> > "disable interrupts; unlink object from cpu cache; enable interrupts"
> > with some window dressing. kfree() is similar.
> >
> > Does it bounce a cache line on freeing perhaps?
>
> I think it's just an assumption that it would be slower. Has anyone
> measured it?

It's likely slower than no kmalloc because
there will be more instructions executed, the question is just how much.

>
> (Note: The measurements I posted do not cover this path, because it was
> on a two cpu system, and it was always using the call-single path.)

Ah so it was already 25% slower even without kmalloc? I thought
that was with already. That doesn't sound good. Any idea where that slowdown
comes from?

-Andi


\
 
 \ /
  Last update: 2008-08-23 09:35    [W:0.276 / U:0.088 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site