From 2e7af192697ef2a71c76fd57860b0fcd02754e14 Mon Sep 17 00:00:00 2001 From: Tommaso Cucinotta Date: Fri, 12 Sep 2025 07:38:29 +0200 Subject: 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 --- include/uapi/linux/sched.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'include/uapi/linux') diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h index 359a14cc76a4..52b69ce89368 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 */ -- cgit v1.2.3