From: Tommaso Cucinotta Date: Fri, 12 Sep 2025 05:38:29 +0000 (+0200) Subject: sched/deadline: Add reporting of runtime left & abs deadline to sched_getattr() for... X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2e7af192697ef2a71c76fd57860b0fcd02754e14;p=thirdparty%2Fkernel%2Flinux.git sched/deadline: Add reporting of runtime left & abs deadline to sched_getattr() for DEADLINE tasks The SCHED_DEADLINE scheduler allows reading the statically configured run-time, deadline, and period parameters through the sched_getattr() system call. However, there is no immediate way to access, from user space, the current parameters used within the scheduler: the instantaneous runtime left in the current cycle, as well as the current absolute deadline. The `flags' sched_getattr() parameter, so far mandated to contain zero, now supports the SCHED_GETATTR_FLAG_DL_DYNAMIC=1 flag, to request retrieval of the leftover runtime and absolute deadline, converted to a CLOCK_MONOTONIC reference, instead of the statically configured parameters. This feature is useful for adaptive SCHED_DEADLINE tasks that need to modify their behavior depending on whether or not there is enough runtime left in the current period, and/or what is the current absolute deadline. Notes: - before returning the instantaneous parameters, the runtime is updated; - the abs deadline is returned shifted from rq_clock() to ktime_get_ns(), in CLOCK_MONOTONIC reference; this causes multiple invocations from the same period to return values that may differ for a few ns (showing some small drift), albeit the deadline doesn't move, in rq_clock() reference; - the abs deadline value returned to user-space, as unsigned 64-bit value, can represent nearly 585 years since boot time; - setting flags=0 provides the old behavior (retrieve static parameters). See also the notes from discussion held at OSPM 2025 on the topic "Making user space aware of current deadline-scheduler parameters". Signed-off-by: Tommaso Cucinotta Signed-off-by: Peter Zijlstra (Intel) Tested-by: Matteo Martelli Link: https://patch.msgid.link/20250912053937.31636-2-tommaso.cucinotta@santannapisa.it --- diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h index 359a14cc76a40..52b69ce893686 100644 --- a/include/uapi/linux/sched.h +++ b/include/uapi/linux/sched.h @@ -146,4 +146,7 @@ struct clone_args { SCHED_FLAG_KEEP_ALL | \ SCHED_FLAG_UTIL_CLAMP) +/* Only for sched_getattr() own flag param, if task is SCHED_DEADLINE */ +#define SCHED_GETATTR_FLAG_DL_DYNAMIC 0x01 + #endif /* _UAPI_LINUX_SCHED_H */ diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 2de5727b94b4f..9e253a825f397 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -3617,13 +3617,26 @@ void __setparam_dl(struct task_struct *p, const struct sched_attr *attr) dl_se->dl_density = to_ratio(dl_se->dl_deadline, dl_se->dl_runtime); } -void __getparam_dl(struct task_struct *p, struct sched_attr *attr) +void __getparam_dl(struct task_struct *p, struct sched_attr *attr, unsigned int flags) { struct sched_dl_entity *dl_se = &p->dl; + struct rq *rq = task_rq(p); + u64 adj_deadline; attr->sched_priority = p->rt_priority; - attr->sched_runtime = dl_se->dl_runtime; - attr->sched_deadline = dl_se->dl_deadline; + if (flags & SCHED_GETATTR_FLAG_DL_DYNAMIC) { + guard(raw_spinlock_irq)(&rq->__lock); + update_rq_clock(rq); + if (task_current(rq, p)) + update_curr_dl(rq); + + attr->sched_runtime = dl_se->runtime; + adj_deadline = dl_se->deadline - rq_clock(rq) + ktime_get_ns(); + attr->sched_deadline = adj_deadline; + } else { + attr->sched_runtime = dl_se->dl_runtime; + attr->sched_deadline = dl_se->dl_deadline; + } attr->sched_period = dl_se->dl_period; attr->sched_flags &= ~SCHED_DL_FLAGS; attr->sched_flags |= dl_se->flags; diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 8bf2f7d524cdf..fa2237e89beea 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -356,7 +356,7 @@ extern int sched_dl_global_validate(void); extern void sched_dl_do_global(void); extern int sched_dl_overflow(struct task_struct *p, int policy, const struct sched_attr *attr); extern void __setparam_dl(struct task_struct *p, const struct sched_attr *attr); -extern void __getparam_dl(struct task_struct *p, struct sched_attr *attr); +extern void __getparam_dl(struct task_struct *p, struct sched_attr *attr, unsigned int flags); extern bool __checkparam_dl(const struct sched_attr *attr); extern bool dl_param_changed(struct task_struct *p, const struct sched_attr *attr); extern int dl_cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial); diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c index 6f10db3646e7f..a288ac0a633d7 100644 --- a/kernel/sched/syscalls.c +++ b/kernel/sched/syscalls.c @@ -881,10 +881,10 @@ err_size: return -E2BIG; } -static void get_params(struct task_struct *p, struct sched_attr *attr) +static void get_params(struct task_struct *p, struct sched_attr *attr, unsigned int flags) { if (task_has_dl_policy(p)) { - __getparam_dl(p, attr); + __getparam_dl(p, attr, flags); } else if (task_has_rt_policy(p)) { attr->sched_priority = p->rt_priority; } else { @@ -950,7 +950,7 @@ SYSCALL_DEFINE3(sched_setattr, pid_t, pid, struct sched_attr __user *, uattr, return -ESRCH; if (attr.sched_flags & SCHED_FLAG_KEEP_PARAMS) - get_params(p, &attr); + get_params(p, &attr, 0); return sched_setattr(p, &attr); } @@ -1035,7 +1035,7 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr, int retval; if (unlikely(!uattr || pid < 0 || usize > PAGE_SIZE || - usize < SCHED_ATTR_SIZE_VER0 || flags)) + usize < SCHED_ATTR_SIZE_VER0)) return -EINVAL; scoped_guard (rcu) { @@ -1043,6 +1043,12 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr, if (!p) return -ESRCH; + if (flags) { + if (!task_has_dl_policy(p) || + flags != SCHED_GETATTR_FLAG_DL_DYNAMIC) + return -EINVAL; + } + retval = security_task_getscheduler(p); if (retval) return retval; @@ -1050,7 +1056,7 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr, kattr.sched_policy = p->policy; if (p->sched_reset_on_fork) kattr.sched_flags |= SCHED_FLAG_RESET_ON_FORK; - get_params(p, &kattr); + get_params(p, &kattr, flags); kattr.sched_flags &= SCHED_FLAG_ALL; #ifdef CONFIG_UCLAMP_TASK