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Message-ID: <20250715164148.1151620-1-tommaso.cucinotta@santannapisa.it>
Date: Tue, 15 Jul 2025 18:39:29 +0200
From: Tommaso Cucinotta <tommaso.cucinotta@...il.com>
To: Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>,
Mel Gorman <mgorman@...e.de>,
Valentin Schneider <vschneid@...hat.com>
Cc: linux-kernel@...r.kernel.org,
linux-api@...r.kernel.org,
Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>
Subject: [PATCH] sched/deadline: sched_getattr(...flags=1) returns the runtime left and abs deadline 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":
https://lwn.net/Articles/1022054/
Signed-off-by: Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>
---
include/uapi/linux/sched.h | 3 +++
kernel/sched/deadline.c | 18 +++++++++++++++---
kernel/sched/sched.h | 2 +-
kernel/sched/syscalls.c | 16 +++++++++++-----
4 files changed, 30 insertions(+), 9 deletions(-)
diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index 359a14cc..52b69ce8 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 9c7d9528..1b5cd7fa 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -3290,13 +3290,25 @@ 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);
+ 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 3058fb62..f69bf019 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -353,7 +353,7 @@ 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 77ae87f3..c80b3568 100644
--- a/kernel/sched/syscalls.c
+++ b/kernel/sched/syscalls.c
@@ -928,10 +928,10 @@ static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *a
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 {
@@ -997,7 +997,7 @@ 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);
}
@@ -1082,7 +1082,7 @@ 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) {
@@ -1090,6 +1090,12 @@ 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;
@@ -1097,7 +1103,7 @@ 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
--
2.45.2
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