[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..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.
 
 
 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

[Juri Lelli]

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

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

[kernel test robot]

Hi Tommaso,

kernel test robot noticed the following build warnings:

[auto build test WARNING on f74d204baf9febf96237af6c1d7eff57fba7de36]

url:    https://github.com/intel-lab-lkp/linux/commits/Tommaso-Cucinotta/sched-deadline-document-new-sched_getattr-feature-for-retrieving-current-parameters-for-DEADLINE-tasks/20260303-184545
base:   f74d204baf9febf96237af6c1d7eff57fba7de36
patch link:    https://lore.kernel.org/r/20260303104215.1324243-1-tommaso.cucinotta%40santannapisa.it
patch subject: [PATCH] sched/deadline: document new sched_getattr() feature for retrieving current parameters for DEADLINE tasks
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
docutils: docutils (Docutils 0.21.2, Python 3.13.5, on linux)
reproduce: (https://download.01.org/0day-ci/archive/20260303/202603031858.JyW2vicC-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202603031858.JyW2vicC-lkp@intel.com/

All warnings (new ones prefixed by >>):

   Checksumming on output with GSO
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ [docutils]
>> Documentation/scheduler/sched-deadline.rst:631: WARNING: Inline interpreted text or phrase reference start-string without end-string. [docutils]
   Documentation/userspace-api/landlock:480: ./security/landlock/errata/abi-4.h:5: ERROR: Unexpected section title.


vim +631 Documentation/scheduler/sched-deadline.rst

   615	
   616	 Specifying a periodic/sporadic task that executes for a given amount of
   617	 runtime at each instance, and that is scheduled according to the urgency of
   618	 its own timing constraints needs, in general, a way of declaring:
   619	
   620	  - a (maximum/typical) instance execution time,
   621	  - a minimum interval between consecutive instances,
   622	  - a time constraint by which each instance must be completed.
   623	
   624	 Therefore:
   625	
   626	  * a new struct sched_attr, containing all the necessary fields is
   627	    provided;
   628	  * the new scheduling related syscalls that manipulate it, i.e.,
   629	    sched_setattr() and sched_getattr() are implemented.
   630	
 > 631	 The leftover runtime and absolute deadline of a SCHED_DEADLINE task can be
   632	 read using the sched_getattr() syscall, setting the last syscall parameter
   633	 `flags' to the SCHED_GETATTR_FLAG_DL_DYNAMIC=1 value. This updates the
   634	 runtime left, converts the absolute deadline in CLOCK_MONOTONIC reference,
   635	 then returns these parameters to user-space. The absolute deadline is
   636	 returned as the number of nanoseconds since the CLOCK_MONOTONIC time
   637	 reference (boot instant), as a u64 in the sched_deadline field of sched_attr,
   638	 which can represent nearly 585 years since boot time (calling sched_getattr()
   639	 with flags=0 causes retrieval of the static parameters instead).
   640	
   641	 For debugging purposes, these parameters can also be retrieved through
   642	 /proc/<pid>/sched (entries dl.runtime and dl.deadline, both values in ns),
   643	 but: this is highly inefficient; the returned runtime left is not updated as
   644	 done by sched_getattr(); the deadline is provided in kernel rq_clock time
   645	 reference, that is not directly usable from user-space.
   646	
   647	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

[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