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

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Date:	Tue, 19 Jan 2016 13:12:50 +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>,
	Frédéric 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 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.

> +	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.

Also, note that -rt cannot actually do _any_ allocations/frees from
STARTING.

Please move the allocs/frees to PREPARE/ONLINE.

> +		break;
> +	case CPU_ONLINE:
> +	case CPU_DEAD:
> +		power_cpu_kfree(cpu);
> +		break;
> +	case CPU_DOWN_PREPARE:
> +		if (power_cpu_exit(cpu))
> +			return NOTIFY_BAD;
> +		break;
> +	default:
> +		break;
> +	}
> +
> +	return NOTIFY_OK;
> +}