Re: [RFT][PATCH 2/2] PM / QoS: Fix device resume latency framework
From: Ramesh Thomas
Date: Fri Nov 03 2017 - 03:50:43 EST
On 2017-11-02 at 00:03:54 +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>
> 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@xxxxxxxxx>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> ---
> Documentation/ABI/testing/sysfs-devices-power | 4 ++-
> drivers/base/cpu.c | 3 +-
> drivers/base/power/domain.c | 2 -
> drivers/base/power/domain_governor.c | 27 ++++++++++++--------------
> drivers/base/power/qos.c | 5 +++-
> drivers/base/power/runtime.c | 2 -
> drivers/base/power/sysfs.c | 25 ++++++++++++++++++++----
> drivers/cpuidle/governors/menu.c | 4 +--
> include/linux/pm_qos.h | 24 +++++++++++++++--------
> 9 files changed, 63 insertions(+), 33 deletions(-)
>
> 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_DEFAULT_VALUE PM_QOS_LATENCY_ANY
> +#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)
>
> @@ -173,7 +174,8 @@ static inline s32 dev_pm_qos_requested_f
> static inline s32 dev_pm_qos_raw_read_value(struct device *dev)
> {
> return IS_ERR_OR_NULL(dev->power.qos) ?
> - 0 : pm_qos_read_value(&dev->power.qos->resume_latency);
> + PM_QOS_RESUME_LATENCY_NO_CONSTRAINT :
> + pm_qos_read_value(&dev->power.qos->resume_latency);
> }
> #else
> static inline enum pm_qos_flags_status __dev_pm_qos_flags(struct device *dev,
> @@ -183,9 +185,9 @@ static inline enum pm_qos_flags_status d
> s32 mask)
> { return PM_QOS_FLAGS_UNDEFINED; }
> static inline s32 __dev_pm_qos_read_value(struct device *dev)
> - { return 0; }
> + { return PM_QOS_RESUME_LATENCY_NO_CONSTRAINT; }
> static inline s32 dev_pm_qos_read_value(struct device *dev)
> - { return 0; }
> + { return PM_QOS_RESUME_LATENCY_NO_CONSTRAINT; }
> static inline int dev_pm_qos_add_request(struct device *dev,
> struct dev_pm_qos_request *req,
> enum dev_pm_qos_req_type type,
> @@ -231,9 +233,15 @@ static inline int dev_pm_qos_expose_late
> { return 0; }
> static inline void dev_pm_qos_hide_latency_tolerance(struct device *dev) {}
>
> -static inline s32 dev_pm_qos_requested_resume_latency(struct device *dev) { return 0; }
> +static inline s32 dev_pm_qos_requested_resume_latency(struct device *dev)
> +{
> + return PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
> +}
> static inline s32 dev_pm_qos_requested_flags(struct device *dev) { return 0; }
> -static inline s32 dev_pm_qos_raw_read_value(struct device *dev) { return 0; }
> +static inline s32 dev_pm_qos_raw_read_value(struct device *dev)
> +{
> + return PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
> +}
> #endif
>
> #endif
> 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/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
> @@ -139,6 +139,9 @@ static int apply_constraint(struct dev_p
>
> switch(req->type) {
> case DEV_PM_QOS_RESUME_LATENCY:
> + if (WARN_ON(value < 0))
> + value = 0;
> +
> ret = pm_qos_update_target(&qos->resume_latency,
> &req->data.pnode, action, value);
> break;
> @@ -189,7 +192,7 @@ 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.
> Index: linux-pm/drivers/base/power/domain.c
> ===================================================================
> --- linux-pm.orig/drivers/base/power/domain.c
> +++ linux-pm/drivers/base/power/domain.c
> @@ -1331,7 +1331,7 @@ static struct generic_pm_domain_data *ge
>
> gpd_data->base.dev = dev;
> gpd_data->td.constraint_changed = true;
> - gpd_data->td.effective_constraint_ns = 0;
> + gpd_data->td.effective_constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
> gpd_data->nb.notifier_call = genpd_dev_pm_qos_notifier;
>
> spin_lock_irq(&dev->power.lock);
> 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
> @@ -26,11 +26,11 @@ static int dev_update_qos_constraint(str
> * to take effect, the device has to be resumed and suspended again.
> */
> constraint_ns = dev_gpd_data(dev)->td.effective_constraint_ns;
> - /* 0 means "no constraint" */
> - if (constraint_ns == 0)
> + if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
> return 0;
>
> - if (constraint_ns < *constraint_ns_p || *constraint_ns_p == 0)
> + if (constraint_ns < *constraint_ns_p ||
> + *constraint_ns_p == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
Check for constraint_ns < *constraint_ns_p should be enough because
PM_QOS_RESUME_LATENCY_NO_CONSTRAINT = S32_MAX which is the largest possible
value, if that can be assumed here.
> *constraint_ns_p = constraint_ns;
>
> return 0;
> @@ -58,12 +58,12 @@ static bool default_suspend_ok(struct de
> }
> td->constraint_changed = false;
> td->cached_suspend_ok = false;
> - td->effective_constraint_ns = -1;
> + td->effective_constraint_ns = 0;
> constraint_ns = __dev_pm_qos_read_value(dev);
Why not initialize td->effective_constraint_ns with what is read by
__dev_pm_qos_read_value()? Even though this value will stay only if false
is returned, in which case it does not matter anyway, it looks like more
meaningful value. Also PM_QOS_RESUME_LATENCY_NO_CONSTRAINT may be ok as it
is initialized with at creation.
>
> spin_unlock_irqrestore(&dev->power.lock, flags);
>
> - if (constraint_ns < 0)
> + if (constraint_ns == 0)
> return false;
>
> constraint_ns *= NSEC_PER_USEC;
This will go wrong if PM_QOS_RESUME_LATENCY_NO_CONSTRAINT was the value
Code below and in dev_update_qos_constraint check for that special value.
May be those places can check PM_QOS_RESUME_LATENCY_NO_CONSTRAINT * NSEC_PER_USEC
There may be other places that this might be an issue
> @@ -76,14 +76,14 @@ static bool default_suspend_ok(struct de
> device_for_each_child(dev, &constraint_ns,
> dev_update_qos_constraint);
>
> - if (constraint_ns == 0) {
> + if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT) {
> /* "No restriction", so the device is allowed to suspend. */
> - td->effective_constraint_ns = 0;
> + td->effective_constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
> td->cached_suspend_ok = true;
> - } else if (WARN_ON(constraint_ns < 0)) {
> + } else if (WARN_ON(constraint_ns == 0)) {
This can never happen as this device will not be suspending if the child had
failed to suspend (only case where this value is possible).
> /*
> - * effective_constraint_ns is negative already and
> - * cached_suspend_ok is false, so return right away.
> + * effective_constraint_ns is 0 already and cached_suspend_ok is
> + * false, so return right away.
> */
> return false;
> } else {
> @@ -156,12 +156,11 @@ static bool __default_power_down_ok(stru
> */
> td = &to_gpd_data(pdd)->td;
> constraint_ns = td->effective_constraint_ns;
> - /* Negative values mean "no suspend at all" */
> - if (WARN_ON(constraint_ns < 0))
> + /* 0 mean "no suspend at all" */
> + if (WARN_ON(constraint_ns == 0))
> return false;
If it did not suspend then it cannot powerdown. This check may not be
very useful here.
>
> - /* 0 means "no constraint" */
> - if (constraint_ns == 0)
> + if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
> continue;
>
> if (constraint_ns <= off_on_time_ns)
>