lkml.org 
[lkml]   [2010]   [Nov]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [thiscpuops upgrade 10/10] Lockless (and preemptless) fastpaths for slub
On 11/24/2010 08:17 AM, Christoph Lameter wrote:
> On Wed, 24 Nov 2010, Pekka Enberg wrote:
>
>>> + /*
>>> + * The transaction ids are globally unique per cpu and per operation on
>>> + * a per cpu queue. Thus they can be guarantee that the cmpxchg_double
>>> + * occurs on the right processor and that there was no operation on the
>>> + * linked list in between.
>>> + */
>>> + tid = c->tid;
>>> + barrier();
>> You're using a compiler barrier after every load from c->tid. Why?
> To make sure that the compiler does not do something like loading the tid
> later. The tid must be obtained before the rest of the information from
> the per cpu slab data is retrieved in order to ensure that we have a
> consistent set of data to operate on.

Isn't that best expressed with ACCESS_ONCE()?

J


\
 
 \ /
  Last update: 2010-11-24 20:39    [W:0.101 / U:0.088 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site