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

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Date:	Thu, 21 Jan 2016 16:10:40 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Huang Rui <ray.huang@....com>
Cc:	Borislav Petkov <bp@...e.de>, Ingo Molnar <mingo@...nel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Robert Richter <rric@...nel.org>,
	Jacob Shin <jacob.w.shin@...il.com>,
	John Stultz <john.stultz@...aro.org>,
	Fr�d�ric Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, spg_linux_kernel@....com,
	x86@...nel.org, Guenter Roeck <linux@...ck-us.net>,
	Andreas Herrmann <herrmann.der.user@...glemail.com>,
	Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
	Aravind Gopalakrishnan <Aravind.Gopalakrishnan@....com>,
	Borislav Petkov <bp@...en8.de>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Aaron Lu <aaron.lu@...el.com>
Subject: Re: [PATCH v2 5/5] perf/x86/amd/power: Add AMD accumulated power
 reporting mechanism

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.

> > > +	cpumask_clear(pmu->mask);
> > > +	cpumask_clear(pmu->tmp_mask);
> > >  
> > >  	for (i = 0; i < cores_per_cu; i++)
> > > +		cpumask_set_cpu(i, pmu->mask);
> > >  
> > > +	cpumask_shift_left(pmu->mask, pmu->mask, cu * cores_per_cu);
> > 
> > Couldn't you simply use topology_sibling_cpumask(cpu) instead?
> > 
> 
> Looks like we couldn't. That's because cores number per cu (compute
> unit) is got by CPUID 0x8000001e EBX. That relies on the CPU hardware.

Borislav? I thought the AMD compute unit stuff was modeled as the SMT
topology.