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Date: Fri, 10 Nov 2017 08:49:31 +0100
From: Ulf Hansson <ulf.hansson@...aro.org>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Linux PM <linux-pm@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
Tero Kristo <t-kristo@...com>,
Reinette Chatre <reinette.chatre@...el.com>,
Ramesh Thomas <ramesh.thomas@...el.com>,
Alex Shi <alex.shi@...aro.org>
Subject: Re: [PATCH v4 2/2] PM / QoS: Fix device resume latency framework
On 7 November 2017 at 11:33, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.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@...el.com>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Tested-by: Reinette Chatre <reinette.chatre@...el.com>
> Tested-by: Geert Uytterhoeven <geert+renesas@...der.be>
Acked-by: Ulf Hansson <ulf.hansson@...aro.org>
Kind regards
Uffe
> ---
>
> As noticed by Ramesh, the v3 had issues with an overlooked value
> conversion and a stale comment, so here goes a v4.
>
> ---
> Documentation/ABI/testing/sysfs-devices-power | 4 +-
> drivers/base/cpu.c | 3 +
> drivers/base/power/domain.c | 2 -
> drivers/base/power/domain_governor.c | 40 ++++++++++----------------
> 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 | 26 +++++++++++-----
> 9 files changed, 68 insertions(+), 43 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
> @@ -28,16 +28,19 @@ 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_LATENCY_ANY_NS ((s64)PM_QOS_LATENCY_ANY * NSEC_PER_USEC)
>
> #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_RESUME_LATENCY_NO_CONSTRAINT_NS PM_QOS_LATENCY_ANY_NS
> #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)
>
> @@ -174,7 +177,8 @@ 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,
> @@ -184,9 +188,9 @@ 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,
> @@ -232,9 +236,15 @@ 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(action != PM_QOS_REMOVE_REQ && 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_NS;
> 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
> @@ -33,15 +33,10 @@ static int dev_update_qos_constraint(str
> * known at this point anyway).
> */
> constraint_ns = dev_pm_qos_read_value(dev);
> - if (constraint_ns > 0)
> - constraint_ns *= NSEC_PER_USEC;
> + constraint_ns *= NSEC_PER_USEC;
> }
>
> - /* 0 means "no constraint" */
> - if (constraint_ns == 0)
> - return 0;
> -
> - if (constraint_ns < *constraint_ns_p || *constraint_ns_p == 0)
> + if (constraint_ns < *constraint_ns_p)
> *constraint_ns_p = constraint_ns;
>
> return 0;
> @@ -69,12 +64,12 @@ 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);
>
> spin_unlock_irqrestore(&dev->power.lock, flags);
>
> - if (constraint_ns < 0)
> + if (constraint_ns == 0)
> return false;
>
> constraint_ns *= NSEC_PER_USEC;
> @@ -87,25 +82,25 @@ 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_NS) {
> /* "No restriction", so the device is allowed to suspend. */
> - td->effective_constraint_ns = 0;
> + td->effective_constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS;
> td->cached_suspend_ok = true;
> - } else if (constraint_ns < 0) {
> + } else if (constraint_ns == 0) {
> /*
> * This triggers if one of the children that don't belong to a
> - * domain has a negative PM QoS constraint and it's better not
> - * to suspend then. effective_constraint_ns is negative already
> - * and cached_suspend_ok is false, so bail out.
> + * domain has a zero PM QoS constraint and it's better not to
> + * suspend then. effective_constraint_ns is zero already and
> + * cached_suspend_ok is false, so bail out.
> */
> return false;
> } else {
> constraint_ns -= td->suspend_latency_ns +
> td->resume_latency_ns;
> /*
> - * effective_constraint_ns is negative already and
> - * cached_suspend_ok is false, so if the computed value is not
> - * positive, return right away.
> + * effective_constraint_ns is zero already and cached_suspend_ok
> + * is false, so if the computed value is not positive, return
> + * right away.
> */
> if (constraint_ns <= 0)
> return false;
> @@ -174,13 +169,10 @@ 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" and this runs only
> - * when all devices in the domain are suspended, so it must be
> - * 0 at least.
> - *
> - * 0 means "no constraint"
> + * Zero means "no suspend at all" and this runs only when all
> + * devices in the domain are suspended, so it must be positive.
> */
> - if (constraint_ns == 0)
> + if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS)
> continue;
>
> if (constraint_ns <= off_on_time_ns)
>
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