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

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Date:	Wed, 20 Jan 2016 12:48:24 +0800
From:	Huang Rui <ray.huang@....com>
To:	Peter Zijlstra <peterz@...radead.org>
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

Hi Peter,

Thanks so much to your comments.

On Tue, Jan 19, 2016 at 01:12:50PM +0100, Peter Zijlstra wrote:
> On Thu, Jan 14, 2016 at 10:50:08AM +0800, Huang Rui wrote:
> > +struct power_pmu {
> > +	spinlock_t		lock;
> 
> This should be a raw_spinlock_t, as it'll be nested under other
> raw_spinlock_t's.
> 

Do you mean the following spinlock operations are in hardware
interrupts disabled case, so I need use raw_spinlock_t instead, right?

Use raw_spin_lock_irqsave/raw_spin_unlock_irqrestore?

> > +	struct list_head	active_list;
> > +	struct pmu		*pmu; /* pointer to power_pmu_class */
> > +	local64_t		cpu_sw_pwr_ptsc;
> > +};
> 
> > +static void pmu_event_start(struct perf_event *event, int mode)
> > +{
> > +	struct power_pmu *pmu = __this_cpu_read(amd_power_pmu);
> > +	unsigned long flags;
> > +
> > +	spin_lock_irqsave(&pmu->lock, flags);
> 
> IRQs will be disabled here.
> 
> > +	__pmu_event_start(pmu, event);
> > +	spin_unlock_irqrestore(&pmu->lock, flags);
> > +}
> > +
> > +static void pmu_event_stop(struct perf_event *event, int mode)
> > +{
> > +	struct power_pmu *pmu = __this_cpu_read(amd_power_pmu);
> > +	struct hw_perf_event *hwc = &event->hw;
> > +	unsigned long flags;
> > +
> > +	spin_lock_irqsave(&pmu->lock, flags);
> 
> idem
> 
> > +
> > +	/* mark event as deactivated and stopped */
> > +	if (!(hwc->state & PERF_HES_STOPPED)) {
> > +		list_del(&event->active_entry);
> > +		hwc->state |= PERF_HES_STOPPED;
> > +	}
> > +
> > +	/* check if update of sw counter is necessary */
> > +	if ((mode & PERF_EF_UPDATE) && !(hwc->state & PERF_HES_UPTODATE)) {
> > +		/*
> > +		 * Drain the remaining delta count out of a event
> > +		 * that we are disabling:
> > +		 */
> > +		event_update(event, pmu);
> > +		hwc->state |= PERF_HES_UPTODATE;
> > +	}
> > +
> > +	spin_unlock_irqrestore(&pmu->lock, flags);
> > +}
> > +
> > +static int pmu_event_add(struct perf_event *event, int mode)
> > +{
> > +	struct power_pmu *pmu = __this_cpu_read(amd_power_pmu);
> > +	struct hw_perf_event *hwc = &event->hw;
> > +	unsigned long flags;
> > +
> > +	spin_lock_irqsave(&pmu->lock, flags);
> > +
> 
> idem
> 
> > +	hwc->state = PERF_HES_UPTODATE | PERF_HES_STOPPED;
> > +
> > +	if (mode & PERF_EF_START)
> > +		__pmu_event_start(pmu, event);
> > +
> > +	spin_unlock_irqrestore(&pmu->lock, flags);
> > +
> > +	return 0;
> > +}
> 
> 
> > +static int power_cpu_init(int cpu)
> > +{
> > +	int i, cu, ret = 0;
> > +	cpumask_var_t mask, dummy_mask;
> > +
> > +	cu = cpu / cores_per_cu;
> > +
> > +	if (!zalloc_cpumask_var(&mask, GFP_KERNEL))
> > +		return -ENOMEM;
> > +
> > +	if (!zalloc_cpumask_var(&dummy_mask, GFP_KERNEL)) {
> > +		ret = -ENOMEM;
> > +		goto out;
> > +	}
> > +
> > +	for (i = 0; i < cores_per_cu; i++)
> > +		cpumask_set_cpu(i, mask);
> > +
> > +	cpumask_shift_left(mask, mask, cu * cores_per_cu);
> > +
> > +	if (!cpumask_and(dummy_mask, mask, &cpu_mask))
> > +		cpumask_set_cpu(cpu, &cpu_mask);
> > +
> > +	free_cpumask_var(dummy_mask);
> > +out:
> > +	free_cpumask_var(mask);
> > +
> > +	return ret;
> > +}
> 
> > +static int power_cpu_notifier(struct notifier_block *self,
> > +			      unsigned long action, void *hcpu)
> > +{
> > +	unsigned int cpu = (long)hcpu;
> > +
> > +	switch (action & ~CPU_TASKS_FROZEN) {
> > +	case CPU_UP_PREPARE:
> > +		if (power_cpu_prepare(cpu))
> > +			return NOTIFY_BAD;
> > +		break;
> > +	case CPU_STARTING:
> > +		if (power_cpu_init(cpu))
> > +			return NOTIFY_BAD;
> 
> this is called with IRQs disabled, which makes those GFP_KERNEL allocs
> above a pretty bad idea.
> 

Right, so should I use GFP_ATOMIC to allocate cpumask here?

> Also, note that -rt cannot actually do _any_ allocations/frees from
> STARTING.
> 
> Please move the allocs/frees to PREPARE/ONLINE.
> 

How about add two cpumask_var_t at power_pmu structure? Then allocate
the two cpumask_var_t (pmu->mask, pmu->dummy_mask), and they can be
also used on power_cpu_init.

Thanks,
Rui