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From c4caa5b973f9cdb4c43edea3c32cda62cdf15b3b Mon Sep 17 00:00:00 2001
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From: Karel Zak <kzak@redhat.com>
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Date: Thu, 1 Oct 2020 11:20:01 +0200
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Subject: [PATCH 44/55] chrt: don't restrict --reset-on-fork, add more info to
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man page
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The flag works (= kernel accepts it) for all scheduling policies
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and sched_getattr() returns the flag for all policies.
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There is no reason for userspace to be more smart than kernel or hide
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the flag when it prints sched_getattr()/sched_getscheduler() results.
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# chrt -v --reset-on-fork --batch 0 /bin/true
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pid 1315019's new scheduling policy: SCHED_BATCH|SCHED_RESET_ON_FORK
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# chrt -v --reset-on-fork --fifo 1 /bin/true
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pid 1315055's new scheduling policy: SCHED_FIFO|SCHED_RESET_ON_FORK
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# chrt -v --reset-on-fork --deadline --sched-period 10000 0 /bin/true
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pid 1315182's new scheduling policy: SCHED_DEADLINE|SCHED_RESET_ON_FORK
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# chrt -v --reset-on-fork --idle 0 /bin/true
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pid 1315247's new scheduling policy: SCHED_IDLE|SCHED_RESET_ON_FORK
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# chrt -v --reset-on-fork --rr 1 /bin/true
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pid 1315275's new scheduling policy: SCHED_RR|SCHED_RESET_ON_FORK
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# chrt -v --reset-on-fork --other 0 /bin/true
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pid 1315311's new scheduling policy: SCHED_OTHER|SCHED_RESET_ON_FORK
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Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=1884194
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Signed-off-by: Karel Zak <kzak@redhat.com>
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---
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schedutils/chrt.1 | 32 ++++++++++++++++++++++++++++----
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schedutils/chrt.c | 18 +++++-------------
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2 files changed, 33 insertions(+), 17 deletions(-)
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diff --git a/schedutils/chrt.1 b/schedutils/chrt.1
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index 4b8b1e9da..a9adfb316 100644
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--- a/schedutils/chrt.1
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+++ b/schedutils/chrt.1
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@@ -92,13 +92,37 @@ Specifies period parameter for SCHED_DEADLINE policy (Linux-specific).
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Specifies deadline parameter for SCHED_DEADLINE policy (Linux-specific).
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.TP
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\fB\-R\fR, \fB\-\-reset-on-fork\fR
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-Add
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+Use
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.B SCHED_RESET_ON_FORK
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-flag to the
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+or
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+.B SCHED_FLAG_RESET_ON_FORK
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+flag. Linux-specific, supported since 2.6.31.
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+
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+Each thread has a reset-on-fork scheduling flag. When this flag is set, children created by
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+.BR fork (2)
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+do not inherit privileged scheduling policies. After the reset-on-fork flag has been enabled,
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+it can be reset only if the thread has the
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+.BR CAP_SYS_NICE
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+capability. This flag is disabled in child processes created by
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+.BR fork (2).
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+
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+More precisely, if the reset-on-fork flag is set,
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+the following rules apply for subsequently created children:
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+.RS
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+.IP * 3
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+If the calling thread has a scheduling policy of
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.B SCHED_FIFO
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or
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-.B SCHED_RR
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-scheduling policy (Linux-specific, supported since 2.6.31).
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+.BR SCHED_RR ,
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+the policy is reset to
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+.BR SCHED_OTHER
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+in child processes.
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+.IP *
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+If the calling process has a negative nice value,
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+the nice value is reset to zero in child processes.
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+.RE
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+
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+
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.SH OPTIONS
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.TP
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diff --git a/schedutils/chrt.c b/schedutils/chrt.c
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index 15556bbad..2a6f1e151 100644
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--- a/schedutils/chrt.c
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+++ b/schedutils/chrt.c
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@@ -152,7 +152,7 @@ static void __attribute__((__noreturn__)) usage(void)
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fputs(USAGE_SEPARATOR, out);
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fputs(_("Scheduling options:\n"), out);
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- fputs(_(" -R, --reset-on-fork set SCHED_RESET_ON_FORK for FIFO or RR\n"), out);
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+ fputs(_(" -R, --reset-on-fork set reset-on-fork flag\n"), out);
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fputs(_(" -T, --sched-runtime <ns> runtime parameter for DEADLINE\n"), out);
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fputs(_(" -P, --sched-period <ns> period parameter for DEADLINE\n"), out);
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fputs(_(" -D, --sched-deadline <ns> deadline parameter for DEADLINE\n"), out);
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@@ -173,22 +173,19 @@ static void __attribute__((__noreturn__)) usage(void)
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static const char *get_policy_name(int policy)
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{
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+#ifdef SCHED_RESET_ON_FORK
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+ policy &= ~SCHED_RESET_ON_FORK;
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+#endif
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switch (policy) {
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case SCHED_OTHER:
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return "SCHED_OTHER";
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case SCHED_FIFO:
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-#ifdef SCHED_RESET_ON_FORK
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- case SCHED_FIFO | SCHED_RESET_ON_FORK:
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-#endif
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return "SCHED_FIFO";
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#ifdef SCHED_IDLE
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case SCHED_IDLE:
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return "SCHED_IDLE";
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#endif
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case SCHED_RR:
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-#ifdef SCHED_RESET_ON_FORK
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- case SCHED_RR | SCHED_RESET_ON_FORK:
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-#endif
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return "SCHED_RR";
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#ifdef SCHED_BATCH
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case SCHED_BATCH:
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@@ -257,7 +254,7 @@ fallback:
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else
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prio = sp.sched_priority;
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# ifdef SCHED_RESET_ON_FORK
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- if (policy == (SCHED_FIFO|SCHED_RESET_ON_FORK) || policy == (SCHED_BATCH|SCHED_RESET_ON_FORK))
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+ if (policy & SCHED_RESET_ON_FORK)
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reset_on_fork = 1;
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# endif
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}
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@@ -515,11 +512,6 @@ int main(int argc, char **argv)
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errno = 0;
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ctl->priority = strtos32_or_err(argv[optind], _("invalid priority argument"));
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-#ifdef SCHED_RESET_ON_FORK
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- if (ctl->reset_on_fork && ctl->policy != SCHED_FIFO && ctl->policy != SCHED_RR)
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- errx(EXIT_FAILURE, _("--reset-on-fork option is supported for "
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- "SCHED_FIFO and SCHED_RR policies only"));
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-#endif
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#ifdef SCHED_DEADLINE
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if ((ctl->runtime || ctl->deadline || ctl->period) && ctl->policy != SCHED_DEADLINE)
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errx(EXIT_FAILURE, _("--sched-{runtime,deadline,period} options "
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--
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2.29.2
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