Messages in this thread | | | From | Suren Baghdasaryan <> | Date | Fri, 20 Jul 2018 20:16:06 -0700 | Subject | Re: [PATCH v2 08/12] sched/core: uclamp: extend cpu's cgroup controller |
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On Fri, Jul 20, 2018 at 7:37 PM, Suren Baghdasaryan <surenb@google.com> wrote: > On Mon, Jul 16, 2018 at 1:29 AM, Patrick Bellasi > <patrick.bellasi@arm.com> wrote: >> The cgroup's CPU controller allows to assign a specified (maximum) >> bandwidth to the tasks of a group. However this bandwidth is defined and >> enforced only on a temporal base, without considering the actual >> frequency a CPU is running on. Thus, the amount of computation completed >> by a task within an allocated bandwidth can be very different depending >> on the actual frequency the CPU is running that task. >> The amount of computation can be affected also by the specific CPU a >> task is running on, especially when running on asymmetric capacity >> systems like Arm's big.LITTLE. >> >> With the availability of schedutil, the scheduler is now able >> to drive frequency selections based on actual task utilization. >> Moreover, the utilization clamping support provides a mechanism to >> bias the frequency selection operated by schedutil depending on >> constraints assigned to the tasks currently RUNNABLE on a CPU. >> >> Give the above mechanisms, it is now possible to extend the cpu >> controller to specify what is the minimum (or maximum) utilization which >> a task is expected (or allowed) to generate. >> Constraints on minimum and maximum utilization allowed for tasks in a >> CPU cgroup can improve the control on the actual amount of CPU bandwidth >> consumed by tasks. >> >> Utilization clamping constraints are useful not only to bias frequency >> selection, when a task is running, but also to better support certain >> scheduler decisions regarding task placement. For example, on >> asymmetric capacity systems, a utilization clamp value can be >> conveniently used to enforce important interactive tasks on more capable >> CPUs or to run low priority and background tasks on more energy >> efficient CPUs. >> >> The ultimate goal of utilization clamping is thus to enable: >> >> - boosting: by selecting an higher capacity CPU and/or higher execution >> frequency for small tasks which are affecting the user >> interactive experience. >> >> - capping: by selecting more energy efficiency CPUs or lower execution >> frequency, for big tasks which are mainly related to >> background activities, and thus without a direct impact on >> the user experience. >> >> Thus, a proper extension of the cpu controller with utilization clamping >> support will make this controller even more suitable for integration >> with advanced system management software (e.g. Android). >> Indeed, an informed user-space can provide rich information hints to the >> scheduler regarding the tasks it's going to schedule. >> >> This patch extends the CPU controller by adding a couple of new >> attributes, util_min and util_max, which can be used to enforce task's >> utilization boosting and capping. Specifically: >> >> - util_min: defines the minimum utilization which should be considered, >> e.g. when schedutil selects the frequency for a CPU while a >> task in this group is RUNNABLE. >> i.e. the task will run at least at a minimum frequency which >> corresponds to the min_util utilization >> >> - util_max: defines the maximum utilization which should be considered, >> e.g. when schedutil selects the frequency for a CPU while a >> task in this group is RUNNABLE. >> i.e. the task will run up to a maximum frequency which >> corresponds to the max_util utilization >> >> These attributes: >> >> a) are available only for non-root nodes, both on default and legacy >> hierarchies >> b) do not enforce any constraints and/or dependency between the parent >> and its child nodes, thus relying on the delegation model and >> permission settings defined by the system management software >> c) allow to (eventually) further restrict task-specific clamps defined >> via sched_setattr(2) >> >> This patch provides the basic support to expose the two new attributes >> and to validate their run-time updates. >> >> Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com> >> Cc: Ingo Molnar <mingo@redhat.com> >> Cc: Peter Zijlstra <peterz@infradead.org> >> Cc: Tejun Heo <tj@kernel.org> >> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> >> Cc: Viresh Kumar <viresh.kumar@linaro.org> >> Cc: Todd Kjos <tkjos@google.com> >> Cc: Joel Fernandes <joelaf@google.com> >> Cc: Juri Lelli <juri.lelli@redhat.com> >> Cc: linux-kernel@vger.kernel.org >> Cc: linux-pm@vger.kernel.org >> --- >> Documentation/admin-guide/cgroup-v2.rst | 25 ++++ >> init/Kconfig | 22 +++ >> kernel/sched/core.c | 186 ++++++++++++++++++++++++ >> kernel/sched/sched.h | 5 + >> 4 files changed, 238 insertions(+) >> >> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst >> index 8a2c52d5c53b..328c011cc105 100644 >> --- a/Documentation/admin-guide/cgroup-v2.rst >> +++ b/Documentation/admin-guide/cgroup-v2.rst >> @@ -904,6 +904,12 @@ controller implements weight and absolute bandwidth limit models for >> normal scheduling policy and absolute bandwidth allocation model for >> realtime scheduling policy. >> >> +Cycles distribution is based, by default, on a temporal base and it >> +does not account for the frequency at which tasks are executed. >> +The (optional) utilization clamping support allows to enforce a minimum >> +bandwidth, which should always be provided by a CPU, and a maximum bandwidth, >> +which should never be exceeded by a CPU. >> + >> WARNING: cgroup2 doesn't yet support control of realtime processes and >> the cpu controller can only be enabled when all RT processes are in >> the root cgroup. Be aware that system management software may already >> @@ -963,6 +969,25 @@ All time durations are in microseconds. >> $PERIOD duration. "max" for $MAX indicates no limit. If only >> one number is written, $MAX is updated. >> >> + cpu.util_min >> + A read-write single value file which exists on non-root cgroups. >> + The default is "0", i.e. no bandwidth boosting. >> + >> + The minimum utilization in the range [0, 1023]. >> + >> + This interface allows reading and setting minimum utilization clamp >> + values similar to the sched_setattr(2). This minimum utilization >> + value is used to clamp the task specific minimum utilization clamp. >> + >> + cpu.util_max >> + A read-write single value file which exists on non-root cgroups. >> + The default is "1023". i.e. no bandwidth clamping >> + >> + The maximum utilization in the range [0, 1023]. >> + >> + This interface allows reading and setting maximum utilization clamp >> + values similar to the sched_setattr(2). This maximum utilization >> + value is used to clamp the task specific maximum utilization clamp. >> >> Memory >> ------ >> diff --git a/init/Kconfig b/init/Kconfig >> index 0a377ad7c166..d7e2b74637ff 100644 >> --- a/init/Kconfig >> +++ b/init/Kconfig >> @@ -792,6 +792,28 @@ config RT_GROUP_SCHED >> >> endif #CGROUP_SCHED >> >> +config UCLAMP_TASK_GROUP >> + bool "Utilization clamping per group of tasks" >> + depends on CGROUP_SCHED >> + depends on UCLAMP_TASK >> + default n >> + help >> + This feature enables the scheduler to track the clamped utilization >> + of each CPU based on RUNNABLE tasks currently scheduled on that CPU. >> + >> + When this option is enabled, the user can specify a min and max >> + CPU bandwidth which is allowed for each single task in a group. >> + The max bandwidth allows to clamp the maximum frequency a task >> + can use, while the min bandwidth allows to define a minimum >> + frequency a task will always use. >> + >> + When task group based utilization clamping is enabled, an eventually >> + specified task-specific clamp value is constrained by the cgroup >> + specified clamp value. Both minimum and maximum task clamping cannot >> + be bigger than the corresponding clamping defined at task group level. >> + >> + If in doubt, say N. >> + >> config CGROUP_PIDS >> bool "PIDs controller" >> help >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> index 0cb6e0aa4faa..30b1d894f978 100644 >> --- a/kernel/sched/core.c >> +++ b/kernel/sched/core.c >> @@ -1227,6 +1227,74 @@ static inline int uclamp_group_get(struct task_struct *p, >> return 0; >> } >> >> +#ifdef CONFIG_UCLAMP_TASK_GROUP >> +/** >> + * init_uclamp_sched_group: initialize data structures required for TG's >> + * utilization clamping >> + */ >> +static inline void init_uclamp_sched_group(void) >> +{ >> + struct uclamp_map *uc_map; >> + struct uclamp_se *uc_se; >> + int group_id; >> + int clamp_id; >> + >> + /* Root TG's is statically assigned to the first clamp group */ >> + group_id = 0; >> + >> + /* Initialize root TG's to default (none) clamp values */ >> + for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id) { >> + uc_map = &uclamp_maps[clamp_id][0]; >> + >> + /* Map root TG's clamp value */ >> + uclamp_group_init(clamp_id, group_id, uclamp_none(clamp_id)); >> + >> + /* Init root TG's clamp group */ >> + uc_se = &root_task_group.uclamp[clamp_id]; >> + uc_se->value = uclamp_none(clamp_id); >> + uc_se->group_id = group_id; >> + >> + /* Attach root TG's clamp group */ >> + uc_map[group_id].se_count = 1; >> + } >> +} >> + >> +/** >> + * alloc_uclamp_sched_group: initialize a new TG's for utilization clamping >> + * @tg: the newly created task group >> + * @parent: its parent task group >> + * >> + * A newly created task group inherits its utilization clamp values, for all >> + * clamp indexes, from its parent task group. >> + * This ensures that its values are properly initialized and that the task >> + * group is accounted in the same parent's group index. >> + * >> + * Return: !0 on error >> + */ >> +static inline int alloc_uclamp_sched_group(struct task_group *tg, >> + struct task_group *parent) >> +{ >> + struct uclamp_se *uc_se; >> + int clamp_id; >> + >> + for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id) { >> + uc_se = &tg->uclamp[clamp_id]; >> + >> + uc_se->value = parent->uclamp[clamp_id].value; >> + uc_se->group_id = UCLAMP_NONE; >> + } >> + >> + return 1; >> +} >> +#else /* CONFIG_UCLAMP_TASK_GROUP */ >> +static inline void init_uclamp_sched_group(void) { } >> +static inline int alloc_uclamp_sched_group(struct task_group *tg, >> + struct task_group *parent) >> +{ >> + return 1; >> +} >> +#endif /* CONFIG_UCLAMP_TASK_GROUP */ >> + >> static inline int __setscheduler_uclamp(struct task_struct *p, >> const struct sched_attr *attr) >> { >> @@ -1289,11 +1357,18 @@ static void __init init_uclamp(void) >> raw_spin_lock_init(&uc_map[group_id].se_lock); >> } >> } >> + >> + init_uclamp_sched_group(); >> } >> >> #else /* CONFIG_UCLAMP_TASK */ >> static inline void uclamp_cpu_get(struct rq *rq, struct task_struct *p) { } >> static inline void uclamp_cpu_put(struct rq *rq, struct task_struct *p) { } >> +static inline int alloc_uclamp_sched_group(struct task_group *tg, >> + struct task_group *parent) >> +{ >> + return 1; >> +} >> static inline int __setscheduler_uclamp(struct task_struct *p, >> const struct sched_attr *attr) >> { >> @@ -6890,6 +6965,9 @@ struct task_group *sched_create_group(struct task_group *parent) >> if (!alloc_rt_sched_group(tg, parent)) >> goto err; >> >> + if (!alloc_uclamp_sched_group(tg, parent)) >> + goto err; >> + >> return tg; >> >> err: >> @@ -7110,6 +7188,88 @@ static void cpu_cgroup_attach(struct cgroup_taskset *tset) >> sched_move_task(task); >> } >> >> +#ifdef CONFIG_UCLAMP_TASK_GROUP >> +static int cpu_util_min_write_u64(struct cgroup_subsys_state *css, >> + struct cftype *cftype, u64 min_value) >> +{ >> + struct task_group *tg; >> + int ret = -EINVAL; >> + >> + if (min_value > SCHED_CAPACITY_SCALE) >> + return -ERANGE; >> + >> + mutex_lock(&uclamp_mutex); >> + rcu_read_lock(); >> + >> + tg = css_tg(css); >> + if (tg->uclamp[UCLAMP_MIN].value == min_value) { >> + ret = 0; >> + goto out; >> + } >> + if (tg->uclamp[UCLAMP_MAX].value < min_value) >> + goto out; >> + > > + tg->uclamp[UCLAMP_MIN].value = min_value; > + ret = 0; > > Are these assignments missing or am I missing something? Same for > cpu_util_max_write_u64(). >
Ah, I see the assignments now in [9/12] patch...
>> +out: >> + rcu_read_unlock(); >> + mutex_unlock(&uclamp_mutex); >> + >> + return ret; >> +} >> + >> +static int cpu_util_max_write_u64(struct cgroup_subsys_state *css, >> + struct cftype *cftype, u64 max_value) >> +{ >> + struct task_group *tg; >> + int ret = -EINVAL; >> + >> + if (max_value > SCHED_CAPACITY_SCALE) >> + return -ERANGE; >> + >> + mutex_lock(&uclamp_mutex); >> + rcu_read_lock(); >> + >> + tg = css_tg(css); >> + if (tg->uclamp[UCLAMP_MAX].value == max_value) { >> + ret = 0; >> + goto out; >> + } >> + if (tg->uclamp[UCLAMP_MIN].value > max_value) >> + goto out; >> + >> +out: >> + rcu_read_unlock(); >> + mutex_unlock(&uclamp_mutex); >> + >> + return ret; >> +} >> + >> +static inline u64 cpu_uclamp_read(struct cgroup_subsys_state *css, >> + enum uclamp_id clamp_id) >> +{ >> + struct task_group *tg; >> + u64 util_clamp; >> + >> + rcu_read_lock(); >> + tg = css_tg(css); >> + util_clamp = tg->uclamp[clamp_id].value; >> + rcu_read_unlock(); >> + >> + return util_clamp; >> +} >> + >> +static u64 cpu_util_min_read_u64(struct cgroup_subsys_state *css, >> + struct cftype *cft) >> +{ >> + return cpu_uclamp_read(css, UCLAMP_MIN); >> +} >> + >> +static u64 cpu_util_max_read_u64(struct cgroup_subsys_state *css, >> + struct cftype *cft) >> +{ >> + return cpu_uclamp_read(css, UCLAMP_MAX); >> +} >> +#endif /* CONFIG_UCLAMP_TASK_GROUP */ >> + >> #ifdef CONFIG_FAIR_GROUP_SCHED >> static int cpu_shares_write_u64(struct cgroup_subsys_state *css, >> struct cftype *cftype, u64 shareval) >> @@ -7437,6 +7597,18 @@ static struct cftype cpu_legacy_files[] = { >> .read_u64 = cpu_rt_period_read_uint, >> .write_u64 = cpu_rt_period_write_uint, >> }, >> +#endif >> +#ifdef CONFIG_UCLAMP_TASK_GROUP >> + { >> + .name = "util_min", >> + .read_u64 = cpu_util_min_read_u64, >> + .write_u64 = cpu_util_min_write_u64, >> + }, >> + { >> + .name = "util_max", >> + .read_u64 = cpu_util_max_read_u64, >> + .write_u64 = cpu_util_max_write_u64, >> + }, >> #endif >> { } /* Terminate */ >> }; >> @@ -7604,6 +7776,20 @@ static struct cftype cpu_files[] = { >> .seq_show = cpu_max_show, >> .write = cpu_max_write, >> }, >> +#endif >> +#ifdef CONFIG_UCLAMP_TASK_GROUP >> + { >> + .name = "util_min", >> + .flags = CFTYPE_NOT_ON_ROOT, >> + .read_u64 = cpu_util_min_read_u64, >> + .write_u64 = cpu_util_min_write_u64, >> + }, >> + { >> + .name = "util_max", >> + .flags = CFTYPE_NOT_ON_ROOT, >> + .read_u64 = cpu_util_max_read_u64, >> + .write_u64 = cpu_util_max_write_u64, >> + }, >> #endif >> { } /* terminate */ >> }; >> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h >> index 7e4f10c507b7..1471a23e8f57 100644 >> --- a/kernel/sched/sched.h >> +++ b/kernel/sched/sched.h >> @@ -389,6 +389,11 @@ struct task_group { >> #endif >> >> struct cfs_bandwidth cfs_bandwidth; >> + >> +#ifdef CONFIG_UCLAMP_TASK_GROUP >> + struct uclamp_se uclamp[UCLAMP_CNT]; >> +#endif >> + >> }; >> >> #ifdef CONFIG_FAIR_GROUP_SCHED >> -- >> 2.17.1 >>
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