[PATCH] chrt: Add support for SCHED_FLAG_DL_OVERRUN

[PATCH] chrt: Add support for SCHED_FLAG_DL_OVERRUN

[Furkan Caliskan]

When set on a SCHED_DEADLINE task, the kernel sends SIGXCPU to the
task if it exceeds its runtime budget within a period. Without this
flag the task is silently throttled until the next period. Useful
for real-time applications that need to detect when they are not
meeting their timing requirements.

Add -O/--deadline-overrun option to allow users to toggle this
feature using the deadline scheduling class.

Signed-off-by: Furkan Caliskan <frn1furkan10@gmail.com>
---
 bash-completion/chrt   |  1 +
 schedutils/chrt.1.adoc |  3 +++
 schedutils/chrt.c      | 17 ++++++++++++++++-
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/bash-completion/chrt b/bash-completion/chrt
index 363efdfa1..ead03b023 100644
--- a/bash-completion/chrt
+++ b/bash-completion/chrt
@@ -19,6 +19,7 @@ _chrt_module()
 				--all-tasks
 				--batch
 				--deadline
+				--deadline-overrun
 				--ext
 				--fifo
 				--help
diff --git a/schedutils/chrt.1.adoc b/schedutils/chrt.1.adoc
index 7c2ceab86..13a785c7e 100644
--- a/schedutils/chrt.1.adoc
+++ b/schedutils/chrt.1.adoc
@@ -85,6 +85,9 @@ Specifies deadline parameter for *SCHED_DEADLINE* policy (Linux-specific).
 *-G*, *--reclaim-grub*::
 Enables GRUB (Greedy Reclamation of Unused Bandwidth) algorithm. Linux-specific, supported since 4.13.
 
+*-O*, *--deadline-overrun*::
+Set *SCHED_FLAG_DL_OVERRUN* to receive *SIGXCPU* when a *SCHED_DEADLINE* task exceeds its runtime budget within a period. Without this flag the task is silently throttled until the next period. Linux-specific, supported since 4.16.
+
 *-R*, *--reset-on-fork*::
 Use *SCHED_RESET_ON_FORK* or *SCHED_FLAG_RESET_ON_FORK* flag. Linux-specific, supported since 2.6.31.
 +
diff --git a/schedutils/chrt.c b/schedutils/chrt.c
index 6bf08c5c1..cec41468a 100644
--- a/schedutils/chrt.c
+++ b/schedutils/chrt.c
@@ -93,6 +93,7 @@ static void __attribute__((__noreturn__)) usage(void)
 	fputs(_("Scheduling options:\n"), out);
 	fputs(_(" -R, --reset-on-fork       set reset-on-fork flag\n"), out);
 	fputs(_(" -G, --reclaim-grub        set SCHED_FLAG_RECLAIM\n"), out);
+	fputs(_(" -O, --deadline-overrun    set SCHED_FLAG_DL_OVERRUN\n"), out);
 	fputs(_(" -T, --sched-runtime <ns>  runtime parameter for DEADLINE\n"), out);
 	fputs(_(" -P, --sched-period <ns>   period parameter for DEADLINE\n"), out);
 	fputs(_(" -D, --sched-deadline <ns> deadline parameter for DEADLINE\n"), out);
@@ -440,6 +441,7 @@ int main(int argc, char **argv)
 		{ "all-tasks",  no_argument, NULL, 'a' },
 		{ "batch",	no_argument, NULL, 'b' },
 		{ "deadline",   no_argument, NULL, 'd' },
+		{ "deadline-overrun", no_argument, NULL, 'O' },
 		{ "ext",	no_argument, NULL, 'e' },
 		{ "fifo",	no_argument, NULL, 'f' },
 		{ "idle",	no_argument, NULL, 'i' },
@@ -463,7 +465,7 @@ int main(int argc, char **argv)
 	textdomain(PACKAGE);
 	close_stdout_atexit();
 
-	while((c = getopt_long(argc, argv, "+abdD:efiphmoP:T:rRGvV", longopts, NULL)) != -1)
+	while((c = getopt_long(argc, argv, "+abdD:efiphmoOP:T:rRGvV", longopts, NULL)) != -1)
 	{
 		switch (c) {
 		case 'a':
@@ -499,6 +501,11 @@ int main(int argc, char **argv)
 		case 'G':
 #ifdef SCHED_FLAG_RECLAIM
 			ctl->sched_flags |= SCHED_FLAG_RECLAIM;
+#endif
+			break;
+		case 'O':
+#ifdef SCHED_FLAG_DL_OVERRUN
+			ctl->sched_flags |= SCHED_FLAG_DL_OVERRUN;
 #endif
 			break;
 		case 'i':
@@ -596,6 +603,14 @@ int main(int argc, char **argv)
 #  endif
 	if ((ctl->sched_flags & SCHED_FLAG_RECLAIM) && ctl->policy != SCHED_DEADLINE)
 		errx(EXIT_FAILURE, _("--reclaim-grub is only supported for SCHED_DEADLINE"));
+# endif
+# ifdef SCHED_FLAG_DL_OVERRUN
+#  ifndef HAVE_SCHED_SETATTR
+	if (ctl->sched_flags & SCHED_FLAG_DL_OVERRUN)
+		errx(EXIT_FAILURE, _("SCHED_FLAG_DL_OVERRUN is unsupported"));
+#  endif
+	if ((ctl->sched_flags & SCHED_FLAG_DL_OVERRUN) && ctl->policy != SCHED_DEADLINE)
+		errx(EXIT_FAILURE, _("--deadline-overrun is only supported for SCHED_DEADLINE"));
 # endif
 	if (ctl->policy == SCHED_DEADLINE) {
 		/* The basic rule is runtime <= deadline <= period, so we can
-- 
2.34.1

Re: [PATCH] chrt: Add support for SCHED_FLAG_DL_OVERRUN

[Karel Zak]

On Wed, May 13, 2026 at 01:01:00PM +0300, Furkan Caliskan wrote:
> When set on a SCHED_DEADLINE task, the kernel sends SIGXCPU to the
> task if it exceeds its runtime budget within a period. Without this
> flag the task is silently throttled until the next period. Useful
> for real-time applications that need to detect when they are not
> meeting their timing requirements.

I have added this to the TODO list:
https://github.com/util-linux/util-linux/issues/4339 ;-)

It seems you (1frn10) already use GitHub. Creating a pull request
there will speed up testing, reviews, and CI.

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com

Re: [PATCH] chrt: Add support for SCHED_FLAG_DL_OVERRUN

[Furkan Çalışkan]

Hi Karel,

On 5/13/26 13:56, Karel Zak wrote:
> On Wed, May 13, 2026 at 01:01:00PM +0300, Furkan Caliskan wrote:
>> When set on a SCHED_DEADLINE task, the kernel sends SIGXCPU to the
>> task if it exceeds its runtime budget within a period. Without this
>> flag the task is silently throttled until the next period. Useful
>> for real-time applications that need to detect when they are not
>> meeting their timing requirements.
> 
> I have added this to the TODO list:
> https://github.com/util-linux/util-linux/issues/4339 ;-)
> 
> It seems you (1frn10) already use GitHub. Creating a pull request
> there will speed up testing, reviews, and CI.
> 
>     Karel
> 

Thanks for the feedback. I have opened a pull request here:
https://github.com/util-linux/util-linux/pull/4347

--
Furkan Caliskan