[PATCH v2] sched/deadline: document new sched_getattr() feature for retrieving current parameters for DEADLINE tasks
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REVIEWED: 1 (1M)
From: Tommaso Cucinotta <hidden>
Date: 2026-03-04 10:29:10
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documentation, the rest · Maintainers:
Jonathan Corbet, Linus Torvalds
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Document in Documentation/sched/sched-deadline.rst the new capability of sched_getattr() to retrieve, for DEADLINE tasks, the runtime left and absolute deadline (setting the flags syscall parameter to 1), in addition to the static parameters (obtained with flags=0). Signed-off-by: Tommaso Cucinotta <redacted> Acked-by: Juri Lelli <juri.lelli@redhat.com> --- Documentation/scheduler/sched-deadline.rst | 19 +++++++++++++++---- 1 file changed, 15 insertions(+), 4 deletions(-)
diff --git a/Documentation/scheduler/sched-deadline.rst b/Documentation/scheduler/sched-deadline.rst
index ec543a12..76fdf435 100644
--- a/Documentation/scheduler/sched-deadline.rst
+++ b/Documentation/scheduler/sched-deadline.rst@@ -628,10 +628,21 @@ Deadline Task Scheduling * the new scheduling related syscalls that manipulate it, i.e., sched_setattr() and sched_getattr() are implemented. - For debugging purposes, the leftover runtime and absolute deadline of a - SCHED_DEADLINE task can be retrieved through /proc/<pid>/sched (entries - dl.runtime and dl.deadline, both values in ns). A programmatic way to - retrieve these values from production code is under discussion. + The leftover runtime and absolute deadline of a SCHED_DEADLINE task can be + read using the sched_getattr() syscall, setting the last syscall parameter + flags to the SCHED_GETATTR_FLAG_DL_DYNAMIC=1 value. This updates the + runtime left, converts the absolute deadline in CLOCK_MONOTONIC reference, + then returns these parameters to user-space. The absolute deadline is + returned as the number of nanoseconds since the CLOCK_MONOTONIC time + reference (boot instant), as a u64 in the sched_deadline field of sched_attr, + which can represent nearly 585 years since boot time (calling sched_getattr() + with flags=0 causes retrieval of the static parameters instead). + + For debugging purposes, these parameters can also be retrieved through + /proc/<pid>/sched (entries dl.runtime and dl.deadline, both values in ns), + but: this is highly inefficient; the returned runtime left is not updated as + done by sched_getattr(); the deadline is provided in kernel rq_clock time + reference, that is not directly usable from user-space. 4.3 Default behavior
base-commit: f74d204baf9febf96237af6c1d7eff57fba7de36 -- 2.45.2