[PATCH] arch/x86/oprofile/op_model_amd.c: perform initialisationon a single CPU

[Robert Richter]

On 30.12.10 12:38:47, Ingo Molnar wrote:
> 
> * Robert Richter <robert.richter@xxxxxxx> wrote:
> 
> > On 29.12.10 11:37:43, Ingo Molnar wrote:
> > 
> > > Hm, i'm not sure this fix is correct:
> > > 
> > >  static int op_amd_init(struct oprofile_operations *ops)
> > >  {
> > > +       /*
> > > +        * init_ibs() preforms implictly cpu-local operations, so pin this
> > > +        * thread to its current CPU
> > > +        */
> > > +       preempt_disable();
> > >         init_ibs();
> > > +       preempt_enable();
> > > 
> > > If init_ibs() is indeed CPU local, then it needs to be called on all CPUs. Does 
> > > that happen and if not why not? AFAICS it's only called on one CPU.
> > 
> > It is correct to run init_ibs() only on one cpu.  It only checks the ibs 
> > capabilities and sets up pci devices (if necessary). It runs only on one cpu but 
> > operates with the local APIC and some MSRs, thus it is better to disable 
> > preemption.
> 
> Ok, but in that case the prempt_disable()/enable() should be put into init_ibs(), 
> not be open-coded at the caller like that.
> 
> The comment about its cpu-localness could move to init_ibs() as well.

Ingo,

the patch below addresses this.  Please apply to tip/perf/urgent.

Thanks,

-Robert

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