Re: [PATCH] sched/deadline: document new sched_getattr() feature for retrieving current parameters for DEADLINE tasks

[Juri Lelli <juri.lelli@redhat.com>]

Hello,

On 03/03/26 11:41, Tommaso Cucinotta wrote:
> 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).

Looks like changelog wasn't properly wrapped?

> Signed-off-by: Tommaso Cucinotta <tommaso.cucinotta@santannapisa.it>
> 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..03970cc8 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.

This looks good to me instead.

Thanks,
Juri