Re: [PATCH v2 5/5] perf/x86/amd/power: Add AMD accumulated power reporting mechanism

[Huang Rui <ray.huang@amd.com>]

On Thu, Jan 21, 2016 at 04:10:40PM +0100, Peter Zijlstra wrote:
> On Thu, Jan 21, 2016 at 10:42:35PM +0800, Huang Rui wrote:
> > > > @@ -164,14 +171,14 @@ static int pmu_event_add(struct perf_event *event, int mode)
> > > >  	struct hw_perf_event *hwc = &event->hw;
> > > >  	unsigned long flags;
> > > >  
> > > > -	spin_lock_irqsave(&pmu->lock, flags);
> > > > +	raw_spin_lock_irqsave(&pmu->lock, flags);
> > > >  
> > > >  	hwc->state = PERF_HES_UPTODATE | PERF_HES_STOPPED;
> > > >  
> > > >  	if (mode & PERF_EF_START)
> > > >  		__pmu_event_start(pmu, event);
> > > >  
> > > > -	spin_unlock_irqrestore(&pmu->lock, flags);
> > > > +	raw_spin_unlock_irqrestore(&pmu->lock, flags);
> > > >  
> > > >  	return 0;
> > > >  }
> > > 
> > > So for these 4 {start,stop,add,del} you can drop the irqsave/irqrestore
> > > thing as its guaranteed that IRQs will be disabled.
> > > 
> > 
> > OK, I will remove the lock.
> 
> No, the lock seems needed, as the list is global. Just the
> irqsave/irqrestore part is superfluous.
> 

But actually, the lock is only used at {start,stop,add,del}. If we
drop irqsave/irqrestore on these 4 things, there won't be any use
cases.

Thanks,
Rui