lkml.org 
[lkml]   [2014]   [Oct]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Why do we still have 32 bit counters? Interrupt counters overflow within 50 days
On Mon, 6 Oct 2014, David Lang wrote:
> On Sun, 5 Oct 2014, Thomas Gleixner wrote:
>
> > >
> > > 64 bit counters on 32 bit machines are not an easy thing and could be
> >
> > Whats so hard about 64bit counters on 32bit machines?
> >
> > > expensive to handle in particular because these counters are used in
> > > performance critical hotpaths.
> >
> > The expensive overhead is a single "adcl" instruction.
>
> As I understand it, since the 64 bit math cannot be made atomic, it requires
> protecting the counter with a lock so that it can't be read while half
> updated. Aquiring a lock on every update is an expensive thing to do. It's not
> something people like to see in a fast path, especially for something of as
> low an importance as the counters.

As I said before. Both reader and writer side are already protected by
the irq descriptor lock. We take that lock anyway.

Thanks,

tglx


\
 
 \ /
  Last update: 2014-10-06 15:02    [W:0.090 / U:0.124 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site