Hi Tommaso, On 15/07/25 18:39, Tommaso Cucinotta wrote: > 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). As we discussed this offline before your submission you know that I was already on board with the idea, so I would really like to hear what Peter and others think about this. Still a few comments below. $SUBJECT can maybe simply be "sched/deadline: Add reporting of remaining time/abs deadline to sched_getattr". > 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/ I would probably remove the link from the changelog as it might disappear/change in the future. > Signed-off-by: Tommaso Cucinotta <tommaso.cucinotta@xxxxxxxxxxxxxxx> > --- > 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); I p is not current maybe we don't need to call update_curr_dl() as p will still have sensible dynamic parameters updated last time it blocked? Also, even though this is superuser stuff and all, mildly fear this could be used as a DOS attack vector? Do we want to be super defensive and add some kind of rate limiting? > + > + 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) Nit pick. Formatting usually has line break after '||'. > + return -EINVAL; > + } > + Thanks! Juri
