From e7a2d62434c22e8de16dcbbeb7b57b0cdcf4bb9a Mon Sep 17 00:00:00 2001 From: Madadi Vineeth Reddy Date: Sun, 22 Jun 2025 01:20:48 +0530 Subject: [PATCH] chrt: Make priority optional for policies that don't use it 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 -o -T 1000000 --pid 0 $PID Passing '0' after --pid is not intutive and not required as priority is not applicable to SCHED_OTHER tasks. Now with this patch, one can do: chrt -o -T 1000000 --pid $PID Passing '0' still works ensuring ABI doesn't break. Signed-off-by: Madadi Vineeth Reddy --- schedutils/chrt.1.adoc | 14 +++++++++----- schedutils/chrt.c | 24 ++++++++++++++++-------- 2 files changed, 25 insertions(+), 13 deletions(-) diff --git a/schedutils/chrt.1.adoc b/schedutils/chrt.1.adoc index 36cdcc5fe..5b8d7e832 100644 --- a/schedutils/chrt.1.adoc +++ b/schedutils/chrt.1.adoc @@ -49,7 +49,7 @@ chrt - manipulate the real-time attributes of a process == POLICIES *-o*, *--other*:: -Set scheduling policy to *SCHED_OTHER* (time-sharing scheduling). This is the default Linux scheduling policy. +Set scheduling policy to *SCHED_OTHER* (time-sharing scheduling). This is the default Linux scheduling policy. Since util-linux v2.42, the priority argument is optional; if specified, it must be set to zero. *-f*, *--fifo*:: Set scheduling policy to *SCHED_FIFO* (first in-first out). @@ -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 --pid 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 --pid* _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 d694845ac..0bcdd1a1e 100644 --- a/schedutils/chrt.c +++ b/schedutils/chrt.c @@ -399,7 +399,7 @@ int main(int argc, char **argv) { struct chrt_ctl _ctl = { .pid = -1, .policy = SCHED_RR }, *ctl = &_ctl; int c; - bool policy_given = false; + bool policy_given = false, need_prio = false; static const struct option longopts[] = { { "all-tasks", no_argument, NULL, 'a' }, @@ -455,6 +455,7 @@ int main(int argc, char **argv) case 'f': ctl->policy = SCHED_FIFO; policy_given = true; + need_prio = true; break; case 'R': ctl->reset_on_fork = 1; @@ -480,6 +481,7 @@ int main(int argc, char **argv) case 'r': ctl->policy = SCHED_RR; policy_given = true; + need_prio = true; break; case 'v': ctl->verbose = 1; @@ -503,29 +505,35 @@ int main(int argc, char **argv) } } - if (((ctl->pid > -1) && argc - optind < 1) || - ((ctl->pid == -1) && argc - optind < 2)) { + 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); } /* pid exists but priority not given */ if (ctl->pid > -1 && argc - optind == 1) { - /* Error if a policy was specified but no priority given */ - if (policy_given) + /* Error if priority is missing for a policy that requires it */ + if (policy_given && need_prio) errx(EXIT_FAILURE, ("policy %s requires a priority argument"), get_policy_name(ctl->policy)); /* If no policy specified, show current settings */ - show_sched_info(ctl); - return EXIT_SUCCESS; + if (!policy_given) { + show_sched_info(ctl); + return EXIT_SUCCESS; + } } if (ctl->verbose) show_sched_info(ctl); 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"), -- 2.47.2