Currently, chrt requires a priority argument even for scheduling
policies like SCHED_OTHER and SCHED_BATCH, which ignore it.
This change relaxes that requirement. Now, priority is only expected
for SCHED_FIFO and SCHED_RR. For other policies, a default value of 0
is set internally and no argument is required on the command line.
This simplifies usage when modifying runtime parameters like
--sched-runtime for non-realtime tasks.
For example, to change the EEVDF tunable base_slice, one currently
needs to run:
chrt -v -o -T 1000000 -p 0 $PID
Passing '0' after -p is not intutive and not required as priority is
not applicable to SCHED_OTHER tasks. Now with this patch, one can do:
chrt -v -o -T 1000000 -p $PID
Passing '0' still works ensuring ABI doesn't break.
Signed-off-by: Madadi Vineeth Reddy <vineethr@xxxxxxxxxxxxx>
---
Changes in v2:
- Updated the man page to reflect the optional priority behavior (Karel Zak)
- Renamed variable to 'need_prio' (Karel Zak)
Signed-off-by: Madadi Vineeth Reddy <vineethr@xxxxxxxxxxxxx>
---
schedutils/chrt.1.adoc | 12 ++++++++----
schedutils/chrt.c | 16 +++++++++++-----
2 files changed, 19 insertions(+), 9 deletions(-)
diff --git a/schedutils/chrt.1.adoc b/schedutils/chrt.1.adoc
index 77add535d..4f419b5f6 100644
--- a/schedutils/chrt.1.adoc
+++ b/schedutils/chrt.1.adoc
@@ -58,16 +58,16 @@ Set scheduling policy to *SCHED_FIFO* (first in-first out).
Set scheduling policy to *SCHED_RR* (round-robin scheduling). When no policy is defined, the *SCHED_RR* is used as the default.
*-b*, *--batch*::
-Set scheduling policy to *SCHED_BATCH* (scheduling batch processes). Linux-specific, supported since 2.6.16. The priority argument has to be set to zero.
+Set scheduling policy to *SCHED_BATCH* (scheduling batch processes). Linux-specific, supported since 2.6.16. Since util-linux v2.42, the priority argument is optional; if specified, it must be set to zero.
*-i*, *--idle*::
-Set scheduling policy to *SCHED_IDLE* (scheduling very low priority jobs). Linux-specific, supported since 2.6.23. The priority argument has to be set to zero.
+Set scheduling policy to *SCHED_IDLE* (scheduling very low priority jobs). Linux-specific, supported since 2.6.23. Since util-linux v2.42, the priority argument is optional; if specified, it must be set to zero.
*-d*, *--deadline*::
-Set scheduling policy to *SCHED_DEADLINE* (sporadic task model deadline scheduling). Linux-specific, supported since 3.14. The priority argument has to be set to zero. See also *--sched-runtime*, *--sched-deadline* and *--sched-period*. The relation between the options required by the kernel is runtime <= deadline <= period. *chrt* copies _period_ to _deadline_ if *--sched-deadline* is not specified and _deadline_ to _runtime_ if *--sched-runtime* is not specified. It means that at least *--sched-period* has to be specified. See *sched*(7) for more details.
+Set scheduling policy to *SCHED_DEADLINE* (sporadic task model deadline scheduling). Linux-specific, supported since 3.14. Since util-linux v2.42, the priority argument is optional; if specified, it must be set to zero. See also *--sched-runtime*, *--sched-deadline* and *--sched-period*. The relation between the options required by the kernel is runtime <= deadline <= period. *chrt* copies _period_ to _deadline_ if *--sched-deadline* is not specified and _deadline_ to _runtime_ if *--sched-runtime* is not specified. It means that at least *--sched-period* has to be specified. See *sched*(7) for more details.
*-d*, *--ext*::
-Set scheduling policy to *SCHED_EXT* (BPF program-defined scheduling). Linux-specific, supported since 6.12. The priority argument has to be set to zero.
+Set scheduling policy to *SCHED_EXT* (BPF program-defined scheduling). Linux-specific, supported since 6.12. Since util-linux v2.42, the priority argument is optional; if specified, it must be set to zero.
== SCHEDULING OPTIONS
@@ -132,6 +132,10 @@ Reset priorities to default for a process{colon}::
____
*chrt -o -p 0* _PID_
____
+Set a custom slice of 1 ms for a SCHED_OTHER task (priority is optional for policies other than SCHED_FIFO and SCHED_RR){colon}::
+____
+*chrt -o -T 1000000 -p* _PID_
+____
See *sched*(7) for a detailed discussion of the different scheduler classes and how they interact.
== PERMISSIONS
diff --git a/schedutils/chrt.c b/schedutils/chrt.c
index cf99935dc..eb1717acc 100644
--- a/schedutils/chrt.c
+++ b/schedutils/chrt.c
@@ -495,20 +495,26 @@ int main(int argc, char **argv)
}
}
- if (((ctl->pid > -1) && argc - optind < 1) ||
- ((ctl->pid == -1) && argc - optind < 2)) {
+ bool need_prio = (ctl->policy == SCHED_FIFO || ctl->policy == SCHED_RR);
+
+ if (((ctl->pid > -1) && argc - optind < (need_prio ? 1 : 0)) ||
+ ((ctl->pid == -1) && argc - optind < (need_prio ? 2 : 1))) {
warnx(_("bad usage"));
errtryhelp(EXIT_FAILURE);
}
- if ((ctl->pid > -1) && (ctl->verbose || argc - optind == 1)) {
+ if ((ctl->pid > -1) && (ctl->verbose || argc - optind == (need_prio ? 1 : 0))) {
show_sched_info(ctl);
- if (argc - optind == 1)
+ if (argc - optind == (need_prio ? 1 : 0))
return EXIT_SUCCESS;
}
errno = 0;
- ctl->priority = strtos32_or_err(argv[optind], _("invalid priority argument"));
+
+ if (need_prio || argc - optind == 2)
+ ctl->priority = strtos32_or_err(argv[optind], _("invalid priority argument"));
+ else
+ ctl->priority = 0;
if (ctl->runtime && !supports_runtime_param(ctl->policy))
errx(EXIT_FAILURE, _("--sched-runtime option is supported for %s"),
--
2.49.0
