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

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

[Tommaso Cucinotta]

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 <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..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

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

[Randy Dunlap]

This patch should be marked as v2, with the differences between
v1 and v2 described.



On 3/3/26 10:42 AM, 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).
> 
> 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..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

About the build warning due to the use of  `flags':
If you want smart quotes, just use 'flags'.
If you want italics, use           `flags`.
If you want a code-look (monotype), use ``flags``.

> + 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

-- 
~Randy

[PATCH v2] sched/deadline: document new sched_getattr() feature for retrieving current parameters for DEADLINE tasks

[Tommaso Cucinotta]

Compared to the initially submitted documentation patch, this
version addresses the issue highlighted by Juri of the wrong wrapping
of the commit message, and the one found by the chatbot of the wrong
use of quotes around the flags parameter. I'm also adding "v2" in
the subject line, as requested by Randy.

[PATCH v2] sched/deadline: document new sched_getattr() feature for retrieving current parameters for DEADLINE tasks

[Tommaso Cucinotta]

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 <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..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

Re: [PATCH v2] sched/deadline: document new sched_getattr() feature for retrieving current parameters for DEADLINE tasks

[Jonathan Corbet]

Tommaso Cucinotta <tommaso.cucinotta@gmail.com> writes:

> 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 <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(-)

Applied, thanks.

jon