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

[Huang Rui]

On Wed, Jan 20, 2016 at 10:22:44AM +0100, Peter Zijlstra wrote:
> On Wed, Jan 20, 2016 at 12:48:24PM +0800, Huang Rui wrote:
> > 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?
> 
> 
> 			mainline		-rt
> 
> raw_spinlock_t		spin-waits		spin-waits
> spinlock_t		spin-waits		blocks (rt-mutex)
> struct mutex		blocks			blocks (rt-mutex)
> 
> 
> since these functions are themselves called with raw_spinlock_t held
> (perf_event_context::lock for example, but also rq::lock), any lock
> nested inside them must also be raw_spinlock_t.
> 

I see, thank you. :-)

I just quickly looked at about the spinlock on -rt mode. Because
realtime linux kernel provides two kinds of spinlock, the original
spinlock_t will be replaced the one which is able to sleep, actually,
like mutex. And another one (you mentioned here, raw_spinlock_t) can
keep on non-sleep behavior, that is the real spinlock.

And my lock here also will be nested under perf_event_context::lock,
right?

> I have a lockdep patch somewhere that checks these ordering things; I
> should rebase and post that again.
> 

Can you CC me when you post that patch next time?

> > Use raw_spin_lock_irqsave/raw_spin_unlock_irqrestore?
> 
> pmu::{start,stop,add,del} will be called with IRQs already disabled.
> 
> > > > +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?
> 
> One should not use GFP_ATOMIC if at all possible, also no, -rt cannot do
> _any_ allocations from this site.
> 

OK, that's because allocation might sleep when IRQ disabled. That's
incorrect.

> > > 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.
> 
> That would work.

I draft an update diff that based on original patch, please take a
look.

8<--------------------------------------------------------------------------

diff --git a/arch/x86/kernel/cpu/perf_event_amd_power.c b/arch/x86/kernel/cpu/perf_event_amd_power.c
index 69ef234..e71d993 100644
--- a/arch/x86/kernel/cpu/perf_event_amd_power.c
+++ b/arch/x86/kernel/cpu/perf_event_amd_power.c
@@ -46,10 +46,17 @@ static unsigned int cu_num;
 static u64 max_cu_acc_power;
 
 struct power_pmu {
-	spinlock_t		lock;
+	raw_spinlock_t		lock;
 	struct list_head	active_list;
 	struct pmu		*pmu; /* pointer to power_pmu_class */
 	local64_t		cpu_sw_pwr_ptsc;
+	/*
+	 * These two cpumasks is used for avoiding the allocations on
+	 * CPU_STARTING phase. Because power_cpu_prepare will be
+	 * called on IRQs disabled status.
+	 */
+	cpumask_var_t		mask;
+	cpumask_var_t		tmp_mask;
 };
 
 static struct pmu pmu_class;
@@ -126,9 +133,9 @@ 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);
+	raw_spin_lock_irqsave(&pmu->lock, flags);
 	__pmu_event_start(pmu, event);
-	spin_unlock_irqrestore(&pmu->lock, flags);
+	raw_spin_unlock_irqrestore(&pmu->lock, flags);
 }
 
 static void pmu_event_stop(struct perf_event *event, int mode)
@@ -137,7 +144,7 @@ static void pmu_event_stop(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);
 
 	/* mark event as deactivated and stopped */
 	if (!(hwc->state & PERF_HES_STOPPED)) {
@@ -155,7 +162,7 @@ static void pmu_event_stop(struct perf_event *event, int mode)
 		hwc->state |= PERF_HES_UPTODATE;
 	}
 
-	spin_unlock_irqrestore(&pmu->lock, flags);
+	raw_spin_unlock_irqrestore(&pmu->lock, flags);
 }
 
 static int pmu_event_add(struct perf_event *event, int mode)
@@ -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;
 }
@@ -297,89 +304,71 @@ static int power_cpu_exit(int cpu)
 	struct power_pmu *pmu = per_cpu(amd_power_pmu, cpu);
 	int i, cu, ret = 0;
 	int target = nr_cpumask_bits;
-	cpumask_var_t mask, tmp_mask;
 
 	cu = cpu / cores_per_cu;
 
-	if (!zalloc_cpumask_var(&mask, GFP_KERNEL))
-		return -ENOMEM;
-
-	if (!zalloc_cpumask_var(&tmp_mask, GFP_KERNEL)) {
-		ret = -ENOMEM;
-		goto out;
-	}
+	cpumask_clear(pmu->mask);
+	cpumask_clear(pmu->tmp_mask);
 
 	for (i = 0; i < cores_per_cu; i++)
-		cpumask_set_cpu(i, mask);
+		cpumask_set_cpu(i, pmu->mask);
 
-	cpumask_shift_left(mask, mask, cu * cores_per_cu);
+	cpumask_shift_left(pmu->mask, pmu->mask, cu * cores_per_cu);
 
 	cpumask_clear_cpu(cpu, &cpu_mask);
-	cpumask_clear_cpu(cpu, mask);
+	cpumask_clear_cpu(cpu, pmu->mask);
 
-	if (!cpumask_and(tmp_mask, mask, cpu_online_mask))
-		goto out1;
+	if (!cpumask_and(pmu->tmp_mask, pmu->mask, cpu_online_mask))
+		goto out;
 
 	/*
 	 * find a new CPU on same compute unit, if was set in cpumask
 	 * and still some CPUs on compute unit, then move to the new
 	 * CPU
 	 */
-	target = cpumask_any(tmp_mask);
+	target = cpumask_any(pmu->tmp_mask);
 	if (target < nr_cpumask_bits && target != cpu)
 		cpumask_set_cpu(target, &cpu_mask);
 
 	WARN_ON(cpumask_empty(&cpu_mask));
 
-out1:
+out:
 	/*
 	 * migrate events and context to new CPU
 	 */
 	if (target < nr_cpumask_bits)
 		perf_pmu_migrate_context(pmu->pmu, cpu, target);
 
-	free_cpumask_var(tmp_mask);
-out:
-	free_cpumask_var(mask);
-
 	return ret;
 
 }
 
 static int power_cpu_init(int cpu)
 {
-	int i, cu, ret = 0;
-	cpumask_var_t mask, dummy_mask;
-
-	cu = cpu / cores_per_cu;
+	struct power_pmu *pmu = per_cpu(amd_power_pmu, cpu);
+	int i, cu;
 
-	if (!zalloc_cpumask_var(&mask, GFP_KERNEL))
-		return -ENOMEM;
+	if (pmu)
+		return 0;
 
-	if (!zalloc_cpumask_var(&dummy_mask, GFP_KERNEL)) {
-		ret = -ENOMEM;
-		goto out;
-	}
+	cu = cpu / cores_per_cu;
 
 	for (i = 0; i < cores_per_cu; i++)
-		cpumask_set_cpu(i, mask);
+		cpumask_set_cpu(i, pmu->mask);
 
-	cpumask_shift_left(mask, mask, cu * cores_per_cu);
+	cpumask_shift_left(pmu->mask, pmu->mask, cu * cores_per_cu);
 
-	if (!cpumask_and(dummy_mask, mask, &cpu_mask))
+	if (!cpumask_and(pmu->tmp_mask, pmu->mask, &cpu_mask))
 		cpumask_set_cpu(cpu, &cpu_mask);
 
-	free_cpumask_var(dummy_mask);
-out:
-	free_cpumask_var(mask);
-
-	return ret;
+	return 0;
 }
 
 static int power_cpu_prepare(int cpu)
 {
 	struct power_pmu *pmu = per_cpu(amd_power_pmu, cpu);
 	int phys_id = topology_physical_package_id(cpu);
+	int ret = 0;
 
 	if (pmu)
 		return 0;
@@ -391,7 +380,17 @@ static int power_cpu_prepare(int cpu)
 	if (!pmu)
 		return -ENOMEM;
 
-	spin_lock_init(&pmu->lock);
+	if (!zalloc_cpumask_var(&pmu->mask, GFP_KERNEL)) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	if (!zalloc_cpumask_var(&pmu->tmp_mask, GFP_KERNEL)) {
+		ret = -ENOMEM;
+		goto out1;
+	}
+
+	raw_spin_lock_init(&pmu->lock);
 
 	INIT_LIST_HEAD(&pmu->active_list);
 
@@ -400,12 +399,21 @@ static int power_cpu_prepare(int cpu)
 	per_cpu(amd_power_pmu, cpu) = pmu;
 
 	return 0;
+
+out1:
+	free_cpumask_var(pmu->mask);
+out:
+	kfree(pmu);
+
+	return ret;
 }
 
 static void power_cpu_kfree(int cpu)
 {
 	struct power_pmu *pmu = per_cpu(amd_power_pmu, cpu);
 
+	free_cpumask_var(pmu->mask);
+	free_cpumask_var(pmu->tmp_mask);
 	kfree(pmu);
 }