lkml.org 
[lkml]   [2013]   [Nov]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC patch 0/5] futex: Allow lockless empty check of hashbucket plist in futex_wake()
On Tue, 26 Nov 2013, Peter Zijlstra wrote:

> On Tue, Nov 26, 2013 at 12:21:40PM +0100, Ingo Molnar wrote:
> > I'm somewhat reluctant to chalk it up to a single mfence - maybe
> > timings/behavior changed in some substantial way?
>
> Ah indeed! We also changed the case where an enqueueing futex sees the
> uval change and bails. It is now far more expensive due to having to
> both queue and unqueue, whereas before it wouldn't queue at all.
>
> I suppose the idea was to offset that by not requiring locking on the
> wake side.

Aside of that I really would be interrested in an explanation for the
STDDEV going up by factor 5. That's a clear indicator for fishyness.

Thanks,

tglx


\
 
 \ /
  Last update: 2013-11-26 14:01    [W:0.057 / U:0.108 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site