diff mbox

[v2] PM / QoS: Fix device resume latency PM QoS

Message ID 1948004.bU45lK7TsE@aspire.rjw.lan (mailing list archive)
State Superseded, archived
Headers show

Commit Message

Rafael J. Wysocki Oct. 24, 2017, 11:35 a.m. UTC 
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

The special value of 0 for device resume latency PM QoS means
"no restriction", but there are two problems with that.

First, device resume latency PM QoS requests with 0 as the
value are always put in front of requests with positive
values in the priority lists used internally by the PM QoS
framework, causing 0 to be chosen as an effective constraint
value.  However, that 0 is then interpreted as "no restriction"
effectively overriding the other requests with specific
restrictions which is incorrect.

Second, the users of device resume latency PM QoS have no
way to specify that *any* resume latency at all should be
avoided, which is an artificial limitation in general.

To address these issues, modify device resume latency PM QoS to
use S32_MAX as the "no constraint" value and 0 as the "no
latency at all" one and rework its users (the cpuidle menu
governor, the genpd QoS governor and the runtime PM framework)
to follow these changes.

Also add a special "n/a" value to the corresponding user space I/F
to allow user space to indicate that it cannot accept any resume
latencies at all for the given device.

Fixes: 85dc0b8a4019 (PM / QoS: Make it possible to expose PM QoS latency constraints)
Link: https://bugzilla.kernel.org/show_bug.cgi?id=197323
Reported-by: Reinette Chatre <reinette.chatre@intel.com>
Tested-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Alex Shi <alex.shi@linaro.org>
---

-> v2: Add a missing "else" branch in pm_qos_resume_latency_store().

---
 Documentation/ABI/testing/sysfs-devices-power |    4 +
 drivers/base/cpu.c                            |    3 -
 drivers/base/power/domain_governor.c          |   53 ++++++++++++++------------
 drivers/base/power/qos.c                      |    2 
 drivers/base/power/runtime.c                  |    2 
 drivers/base/power/sysfs.c                    |   25 ++++++++++--
 drivers/cpuidle/governors/menu.c              |    4 -
 include/linux/pm_qos.h                        |    5 +-
 8 files changed, 63 insertions(+), 35 deletions(-)

Comments

Ramesh Thomas Oct. 25, 2017, 7:16 a.m. UTC | #1 
On 2017-10-24 at 13:35:05 +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 

[cut]

> @@ -63,10 +60,14 @@ static bool default_suspend_ok(struct de
>  
>  	spin_unlock_irqrestore(&dev->power.lock, flags);
>  
> -	if (constraint_ns < 0)
> +	if (constraint_ns == 0)
>  		return false;
>  
> -	constraint_ns *= NSEC_PER_USEC;
> +	if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
> +		constraint_ns = -1;
> +	else
> +		constraint_ns *= NSEC_PER_USEC;
> +
>  	/*
>  	 * We can walk the children without any additional locking, because
>  	 * they all have been suspended at this point and their
> @@ -76,14 +77,19 @@ static bool default_suspend_ok(struct de
>  		device_for_each_child(dev, &constraint_ns,
>  				      dev_update_qos_constraint);
>  
> -	if (constraint_ns > 0) {
> -		constraint_ns -= td->suspend_latency_ns +
> -				td->resume_latency_ns;
> -		if (constraint_ns == 0)
> -			return false;
> +	if (constraint_ns < 0) {
> +		/* The children have no constraints. */
> +		td->effective_constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
> +		td->cached_suspend_ok = true;
> +	} else {
> +		constraint_ns -= td->suspend_latency_ns + td->resume_latency_ns;
> +		if (constraint_ns > 0) {
> +			td->effective_constraint_ns = constraint_ns;
> +			td->cached_suspend_ok = true;
> +		} else {
> +			td->effective_constraint_ns = 0;

If the resume latency constraint was increased after this,
default_power_down_ok may not consider the new value. default_suspend_ok needs
to get called first if the new value is to be read.

This is because dev_pm_qos_read_value will get called only if
effective_constraint_ns has a negative value. default_suspend_ok initializes
effective_constraint_ns with -1 before doing the calculations.
default_power_down_ok does not initialize it to -1 and uses
the existing value.

A comment in default_power_down_ok implies it is not necessary to call
default_suspend_ok before calling default_power_down_ok. In that case,
default_power_down_ok should be able to get the new latency constraint value.


> +		}
>  	}
> -	td->effective_constraint_ns = constraint_ns;
> -	td->cached_suspend_ok = constraint_ns >= 0;
>  
>  	/*
>  	 * The children have been suspended already, so we don't need to take
> @@ -145,13 +151,14 @@ static bool __default_power_down_ok(stru
>  		td = &to_gpd_data(pdd)->td;
>  		constraint_ns = td->effective_constraint_ns;
>  		/* default_suspend_ok() need not be called before us. */
> -		if (constraint_ns < 0) {
> +		if (constraint_ns < 0)
>  			constraint_ns = dev_pm_qos_read_value(pdd->dev);
> -			constraint_ns *= NSEC_PER_USEC;
> -		}
> -		if (constraint_ns == 0)
> +
> +		if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
>  			continue;
>  
> +		constraint_ns *= NSEC_PER_USEC;
> +
>  		/*
>  		 * constraint_ns cannot be negative here, because the device has
>  		 * been suspended.
Ramesh Thomas Oct. 26, 2017, 2 a.m. UTC | #2 
On 2017-10-25 at 00:16:25 -0700, Ramesh Thomas wrote:
> On 2017-10-24 at 13:35:05 +0200, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > 
> 
> [cut]
> 
> > @@ -63,10 +60,14 @@ static bool default_suspend_ok(struct de
> >  
> >  	spin_unlock_irqrestore(&dev->power.lock, flags);
> >  
> > -	if (constraint_ns < 0)
> > +	if (constraint_ns == 0)
> >  		return false;
> >  
> > -	constraint_ns *= NSEC_PER_USEC;
> > +	if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
> > +		constraint_ns = -1;
> > +	else
> > +		constraint_ns *= NSEC_PER_USEC;
> > +
> >  	/*
> >  	 * We can walk the children without any additional locking, because
> >  	 * they all have been suspended at this point and their
> > @@ -76,14 +77,19 @@ static bool default_suspend_ok(struct de
> >  		device_for_each_child(dev, &constraint_ns,
> >  				      dev_update_qos_constraint);
> >  
> > -	if (constraint_ns > 0) {
> > -		constraint_ns -= td->suspend_latency_ns +
> > -				td->resume_latency_ns;
> > -		if (constraint_ns == 0)
> > -			return false;
> > +	if (constraint_ns < 0) {
> > +		/* The children have no constraints. */
> > +		td->effective_constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
> > +		td->cached_suspend_ok = true;
> > +	} else {
> > +		constraint_ns -= td->suspend_latency_ns + td->resume_latency_ns;
> > +		if (constraint_ns > 0) {
> > +			td->effective_constraint_ns = constraint_ns;
> > +			td->cached_suspend_ok = true;
> > +		} else {
> > +			td->effective_constraint_ns = 0;
> 
> If the resume latency constraint was increased after this,
> default_power_down_ok may not consider the new value. default_suspend_ok needs
> to get called first if the new value is to be read.
> 
> This is because dev_pm_qos_read_value will get called only if
> effective_constraint_ns has a negative value. default_suspend_ok initializes
> effective_constraint_ns with -1 before doing the calculations.
> default_power_down_ok does not initialize it to -1 and uses
> the existing value.
> 
> A comment in default_power_down_ok implies it is not necessary to call
> default_suspend_ok before calling default_power_down_ok. In that case,
> default_power_down_ok should be able to get the new latency constraint value.
> 

The design expects default_suspend_ok would always be called before
default_power_down_ok if the device was made "active" after start. Changes
to resume latency constraint will not be considered if it happened between
suspend and power down of a device. However, that is the design and not a
behavior introduced by this patch.

Acked-by: Ramesh Thomas <ramesh.thomas@intel.com>
Rafael J. Wysocki Oct. 26, 2017, 8:44 a.m. UTC | #3 
On Thu, Oct 26, 2017 at 4:00 AM, Ramesh Thomas <ramesh.thomas@intel.com> wrote:
> On 2017-10-25 at 00:16:25 -0700, Ramesh Thomas wrote:
>> On 2017-10-24 at 13:35:05 +0200, Rafael J. Wysocki wrote:
>> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>> >
>>
>> [cut]
>>
>> > @@ -63,10 +60,14 @@ static bool default_suspend_ok(struct de
>> >
>> >     spin_unlock_irqrestore(&dev->power.lock, flags);
>> >
>> > -   if (constraint_ns < 0)
>> > +   if (constraint_ns == 0)
>> >             return false;
>> >
>> > -   constraint_ns *= NSEC_PER_USEC;
>> > +   if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
>> > +           constraint_ns = -1;
>> > +   else
>> > +           constraint_ns *= NSEC_PER_USEC;
>> > +
>> >     /*
>> >      * We can walk the children without any additional locking, because
>> >      * they all have been suspended at this point and their
>> > @@ -76,14 +77,19 @@ static bool default_suspend_ok(struct de
>> >             device_for_each_child(dev, &constraint_ns,
>> >                                   dev_update_qos_constraint);
>> >
>> > -   if (constraint_ns > 0) {
>> > -           constraint_ns -= td->suspend_latency_ns +
>> > -                           td->resume_latency_ns;
>> > -           if (constraint_ns == 0)
>> > -                   return false;
>> > +   if (constraint_ns < 0) {
>> > +           /* The children have no constraints. */
>> > +           td->effective_constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
>> > +           td->cached_suspend_ok = true;
>> > +   } else {
>> > +           constraint_ns -= td->suspend_latency_ns + td->resume_latency_ns;
>> > +           if (constraint_ns > 0) {
>> > +                   td->effective_constraint_ns = constraint_ns;
>> > +                   td->cached_suspend_ok = true;
>> > +           } else {
>> > +                   td->effective_constraint_ns = 0;
>>
>> If the resume latency constraint was increased after this,
>> default_power_down_ok may not consider the new value. default_suspend_ok needs
>> to get called first if the new value is to be read.
>>
>> This is because dev_pm_qos_read_value will get called only if
>> effective_constraint_ns has a negative value. default_suspend_ok initializes
>> effective_constraint_ns with -1 before doing the calculations.
>> default_power_down_ok does not initialize it to -1 and uses
>> the existing value.
>>
>> A comment in default_power_down_ok implies it is not necessary to call
>> default_suspend_ok before calling default_power_down_ok. In that case,
>> default_power_down_ok should be able to get the new latency constraint value.
>>
>
> The design expects default_suspend_ok would always be called before
> default_power_down_ok if the device was made "active" after start. Changes
> to resume latency constraint will not be considered if it happened between
> suspend and power down of a device. However, that is the design and not a
> behavior introduced by this patch.
>
> Acked-by: Ramesh Thomas <ramesh.thomas@intel.com>

Cool, thanks!

I'll go ahead and push this to Linus, then.

Thanks,
Rafael
diff mbox

Patch

Index: linux-pm/drivers/base/power/sysfs.c
===================================================================
--- linux-pm.orig/drivers/base/power/sysfs.c
+++ linux-pm/drivers/base/power/sysfs.c
@@ -218,7 +218,14 @@  static ssize_t pm_qos_resume_latency_sho
 					  struct device_attribute *attr,
 					  char *buf)
 {
-	return sprintf(buf, "%d\n", dev_pm_qos_requested_resume_latency(dev));
+	s32 value = dev_pm_qos_requested_resume_latency(dev);
+
+	if (value == 0)
+		return sprintf(buf, "n/a\n");
+	else if (value == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
+		value = 0;
+
+	return sprintf(buf, "%d\n", value);
 }
 
 static ssize_t pm_qos_resume_latency_store(struct device *dev,
@@ -228,11 +235,21 @@  static ssize_t pm_qos_resume_latency_sto
 	s32 value;
 	int ret;
 
-	if (kstrtos32(buf, 0, &value))
-		return -EINVAL;
+	if (!kstrtos32(buf, 0, &value)) {
+		/*
+		 * Prevent users from writing negative or "no constraint" values
+		 * directly.
+		 */
+		if (value < 0 || value == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
+			return -EINVAL;
 
-	if (value < 0)
+		if (value == 0)
+			value = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
+	} else if (!strcmp(buf, "n/a") || !strcmp(buf, "n/a\n")) {
+		value = 0;
+	} else  {
 		return -EINVAL;
+	}
 
 	ret = dev_pm_qos_update_request(dev->power.qos->resume_latency_req,
 					value);
Index: linux-pm/include/linux/pm_qos.h
===================================================================
--- linux-pm.orig/include/linux/pm_qos.h
+++ linux-pm/include/linux/pm_qos.h
@@ -27,16 +27,17 @@  enum pm_qos_flags_status {
 	PM_QOS_FLAGS_ALL,
 };
 
-#define PM_QOS_DEFAULT_VALUE -1
+#define PM_QOS_DEFAULT_VALUE	(-1)
+#define PM_QOS_LATENCY_ANY	S32_MAX
 
 #define PM_QOS_CPU_DMA_LAT_DEFAULT_VALUE	(2000 * USEC_PER_SEC)
 #define PM_QOS_NETWORK_LAT_DEFAULT_VALUE	(2000 * USEC_PER_SEC)
 #define PM_QOS_NETWORK_THROUGHPUT_DEFAULT_VALUE	0
 #define PM_QOS_MEMORY_BANDWIDTH_DEFAULT_VALUE	0
 #define PM_QOS_RESUME_LATENCY_DEFAULT_VALUE	0
+#define PM_QOS_RESUME_LATENCY_NO_CONSTRAINT	PM_QOS_LATENCY_ANY
 #define PM_QOS_LATENCY_TOLERANCE_DEFAULT_VALUE	0
 #define PM_QOS_LATENCY_TOLERANCE_NO_CONSTRAINT	(-1)
-#define PM_QOS_LATENCY_ANY			((s32)(~(__u32)0 >> 1))
 
 #define PM_QOS_FLAG_NO_POWER_OFF	(1 << 0)
 #define PM_QOS_FLAG_REMOTE_WAKEUP	(1 << 1)
Index: linux-pm/drivers/cpuidle/governors/menu.c
===================================================================
--- linux-pm.orig/drivers/cpuidle/governors/menu.c
+++ linux-pm/drivers/cpuidle/governors/menu.c
@@ -298,8 +298,8 @@  static int menu_select(struct cpuidle_dr
 		data->needs_update = 0;
 	}
 
-	/* resume_latency is 0 means no restriction */
-	if (resume_latency && resume_latency < latency_req)
+	if (resume_latency < latency_req &&
+	    resume_latency != PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
 		latency_req = resume_latency;
 
 	/* Special case when user has set very strict latency requirement */
Index: linux-pm/drivers/base/power/domain_governor.c
===================================================================
--- linux-pm.orig/drivers/base/power/domain_governor.c
+++ linux-pm/drivers/base/power/domain_governor.c
@@ -14,23 +14,20 @@ 
 static int dev_update_qos_constraint(struct device *dev, void *data)
 {
 	s64 *constraint_ns_p = data;
-	s32 constraint_ns = -1;
+	s64 constraint_ns = -1;
 
 	if (dev->power.subsys_data && dev->power.subsys_data->domain_data)
 		constraint_ns = dev_gpd_data(dev)->td.effective_constraint_ns;
 
-	if (constraint_ns < 0) {
+	if (constraint_ns < 0)
 		constraint_ns = dev_pm_qos_read_value(dev);
-		constraint_ns *= NSEC_PER_USEC;
-	}
-	if (constraint_ns == 0)
+
+	if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
 		return 0;
 
-	/*
-	 * constraint_ns cannot be negative here, because the device has been
-	 * suspended.
-	 */
-	if (constraint_ns < *constraint_ns_p || *constraint_ns_p == 0)
+	constraint_ns *= NSEC_PER_USEC;
+
+	if (constraint_ns < *constraint_ns_p || *constraint_ns_p < 0)
 		*constraint_ns_p = constraint_ns;
 
 	return 0;
@@ -63,10 +60,14 @@  static bool default_suspend_ok(struct de
 
 	spin_unlock_irqrestore(&dev->power.lock, flags);
 
-	if (constraint_ns < 0)
+	if (constraint_ns == 0)
 		return false;
 
-	constraint_ns *= NSEC_PER_USEC;
+	if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
+		constraint_ns = -1;
+	else
+		constraint_ns *= NSEC_PER_USEC;
+
 	/*
 	 * We can walk the children without any additional locking, because
 	 * they all have been suspended at this point and their
@@ -76,14 +77,19 @@  static bool default_suspend_ok(struct de
 		device_for_each_child(dev, &constraint_ns,
 				      dev_update_qos_constraint);
 
-	if (constraint_ns > 0) {
-		constraint_ns -= td->suspend_latency_ns +
-				td->resume_latency_ns;
-		if (constraint_ns == 0)
-			return false;
+	if (constraint_ns < 0) {
+		/* The children have no constraints. */
+		td->effective_constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
+		td->cached_suspend_ok = true;
+	} else {
+		constraint_ns -= td->suspend_latency_ns + td->resume_latency_ns;
+		if (constraint_ns > 0) {
+			td->effective_constraint_ns = constraint_ns;
+			td->cached_suspend_ok = true;
+		} else {
+			td->effective_constraint_ns = 0;
+		}
 	}
-	td->effective_constraint_ns = constraint_ns;
-	td->cached_suspend_ok = constraint_ns >= 0;
 
 	/*
 	 * The children have been suspended already, so we don't need to take
@@ -145,13 +151,14 @@  static bool __default_power_down_ok(stru
 		td = &to_gpd_data(pdd)->td;
 		constraint_ns = td->effective_constraint_ns;
 		/* default_suspend_ok() need not be called before us. */
-		if (constraint_ns < 0) {
+		if (constraint_ns < 0)
 			constraint_ns = dev_pm_qos_read_value(pdd->dev);
-			constraint_ns *= NSEC_PER_USEC;
-		}
-		if (constraint_ns == 0)
+
+		if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
 			continue;
 
+		constraint_ns *= NSEC_PER_USEC;
+
 		/*
 		 * constraint_ns cannot be negative here, because the device has
 		 * been suspended.
Index: linux-pm/drivers/base/power/runtime.c
===================================================================
--- linux-pm.orig/drivers/base/power/runtime.c
+++ linux-pm/drivers/base/power/runtime.c
@@ -253,7 +253,7 @@  static int rpm_check_suspend_allowed(str
 	    || (dev->power.request_pending
 			&& dev->power.request == RPM_REQ_RESUME))
 		retval = -EAGAIN;
-	else if (__dev_pm_qos_read_value(dev) < 0)
+	else if (__dev_pm_qos_read_value(dev) == 0)
 		retval = -EPERM;
 	else if (dev->power.runtime_status == RPM_SUSPENDED)
 		retval = 1;
Index: linux-pm/drivers/base/cpu.c
===================================================================
--- linux-pm.orig/drivers/base/cpu.c
+++ linux-pm/drivers/base/cpu.c
@@ -377,7 +377,8 @@  int register_cpu(struct cpu *cpu, int nu
 
 	per_cpu(cpu_sys_devices, num) = &cpu->dev;
 	register_cpu_under_node(num, cpu_to_node(num));
-	dev_pm_qos_expose_latency_limit(&cpu->dev, 0);
+	dev_pm_qos_expose_latency_limit(&cpu->dev,
+					PM_QOS_RESUME_LATENCY_NO_CONSTRAINT);
 
 	return 0;
 }
Index: linux-pm/drivers/base/power/qos.c
===================================================================
--- linux-pm.orig/drivers/base/power/qos.c
+++ linux-pm/drivers/base/power/qos.c
@@ -189,7 +189,7 @@  static int dev_pm_qos_constraints_alloca
 	plist_head_init(&c->list);
 	c->target_value = PM_QOS_RESUME_LATENCY_DEFAULT_VALUE;
 	c->default_value = PM_QOS_RESUME_LATENCY_DEFAULT_VALUE;
-	c->no_constraint_value = PM_QOS_RESUME_LATENCY_DEFAULT_VALUE;
+	c->no_constraint_value = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
 	c->type = PM_QOS_MIN;
 	c->notifiers = n;
 
Index: linux-pm/Documentation/ABI/testing/sysfs-devices-power
===================================================================
--- linux-pm.orig/Documentation/ABI/testing/sysfs-devices-power
+++ linux-pm/Documentation/ABI/testing/sysfs-devices-power
@@ -211,7 +211,9 @@  Description:
 		device, after it has been suspended at run time, from a resume
 		request to the moment the device will be ready to process I/O,
 		in microseconds.  If it is equal to 0, however, this means that
-		the PM QoS resume latency may be arbitrary.
+		the PM QoS resume latency may be arbitrary and the special value
+		"n/a" means that user space cannot accept any resume latency at
+		all for the given device.
 
 		Not all drivers support this attribute.  If it isn't supported,
 		it is not present.