lkml.org 
[lkml]   [2011]   [Feb]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH RFC tip/core/rcu 11/11] rcu: move TREE_RCU from softirq to kthread
* Christoph Lameter (cl@linux.com) wrote:
> On Wed, 23 Feb 2011, Mathieu Desnoyers wrote:
>
> > > > > +
> > > > > + local_irq_save(flags);
> > > > > + cpu = smp_processor_id();
>
> Drop this line.
>
> > > > > + if (per_cpu(rcu_cpu_kthread_task, cpu) == NULL) {
>
> use this_cpu_read(rcu_cpu_kthread_task)
>
> > > > > + local_irq_restore(flags);
> > > > > + return;
> > > > > + }
> > > > > + per_cpu(rcu_cpu_has_work, cpu) = 1;
>
> this_cpu_write(rcu_cpu_has_work, 1);
>
> > This is not quite true on x86_64 and s390 anymore. __get_cpu_var() now
> > uses a segment selector override to get the local CPU variable on x86.
> > See x86's percpu.h for details.
>
> __get_cpu_var cannot use a segment override since there are places where
> the address of the variable is taken. One needs to use this_cpu_ops for
> that.

Ah, thanks for the clarification :)

>
>
> > > True, but we could also argue that the multiple checks for being preempt
> > > can also be an issue.
> >
> > At least on x86 preemption don't actually need to be disabled: selection
> > of the right per-cpu memory location is done atomically with the rest of
> > the instruction by the segment selector.
>
> Right.

Thanks,

Mathieu

--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com


\
 
 \ /
  Last update: 2011-02-23 19:29    [W:0.376 / U:0.044 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site