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Date: Thu, 21 Jan 2016 16:51:20 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Huang Rui <ray.huang@amd.com>
Cc: Borislav Petkov <bp@suse.de>, Ingo Molnar <mingo@kernel.org>,
        Andy Lutomirski <luto@amacapital.net>,
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        Borislav Petkov <bp@alien8.de>, Fengguang Wu <fengguang.wu@intel.com>,
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Subject: Re: [PATCH v2 5/5] perf/x86/amd/power: Add AMD accumulated power
 reporting mechanism
Message-ID: <20160121155120.GI6357@twins.programming.kicks-ass.net>
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On Thu, Jan 21, 2016 at 11:24:14PM +0800, Huang Rui wrote:
> 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.

But, but, the list is global !? something needs to serialize the access
to it, right?