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chrt: don't restrict --reset-on-fork, add more info to man page 

The flag works (= kernel accepts it) for all scheduling policies
and sched_getattr() returns the flag for all policies.

There is no reason for userspace to be more smart than kernel or hide
the flag when it prints sched_getattr()/sched_getscheduler() results.

 # chrt -v --reset-on-fork --batch 0 /bin/true
 pid 1315019's new scheduling policy: SCHED_BATCH|SCHED_RESET_ON_FORK

 # chrt -v --reset-on-fork --fifo 1 /bin/true
 pid 1315055's new scheduling policy: SCHED_FIFO|SCHED_RESET_ON_FORK

 # chrt -v --reset-on-fork --deadline --sched-period 10000 0 /bin/true
 pid 1315182's new scheduling policy: SCHED_DEADLINE|SCHED_RESET_ON_FORK

 # chrt -v --reset-on-fork --idle 0 /bin/true
 pid 1315247's new scheduling policy: SCHED_IDLE|SCHED_RESET_ON_FORK

 # chrt -v --reset-on-fork --rr 1 /bin/true
 pid 1315275's new scheduling policy: SCHED_RR|SCHED_RESET_ON_FORK

 # chrt -v --reset-on-fork --other 0 /bin/true
 pid 1315311's new scheduling policy: SCHED_OTHER|SCHED_RESET_ON_FORK

Signed-off-by: Karel Zak <kzak@redhat.com>
This commit is contained in:
Karel Zak 2020-10-01 11:20:01 +02:00
parent fb4f1da4e0
commit 865f5f469c
2 changed files with 33 additions and 17 deletions
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32
schedutils/chrt.1
View File

@ -86,13 +86,37 @@ Specifies period parameter for SCHED_DEADLINE policy (Linux-specific).
Specifies deadline parameter for SCHED_DEADLINE policy (Linux-specific).
.TP
\fB\-R\fR, \fB\-\-reset-on-fork\fR
Add
Use
.B SCHED_RESET_ON_FORK
flag to the
or
.B SCHED_FLAG_RESET_ON_FORK
flag. Linux-specific, supported since 2.6.31.
Each thread has a reset-on-fork scheduling flag. When this flag is set, children created by
.BR fork (2)
do not inherit privileged scheduling policies. After the reset-on-fork flag has been enabled,
it can be reset only if the thread has the
.BR CAP_SYS_NICE
capability. This flag is disabled in child processes created by
.BR fork (2).
More precisely, if the reset-on-fork flag is set,
the following rules apply for subsequently created children:
.RS
.IP * 3
If the calling thread has a scheduling policy of
.B SCHED_FIFO
or
.B SCHED_RR
scheduling policy (Linux-specific, supported since 2.6.31).
.BR SCHED_RR ,
the policy is reset to
.BR SCHED_OTHER
in child processes.
.IP *
If the calling process has a negative nice value,
the nice value is reset to zero in child processes.
.RE
.SH OPTIONS
.TP

18
schedutils/chrt.c
View File

@ -152,7 +152,7 @@ static void __attribute__((__noreturn__)) usage(void)
fputs(USAGE_SEPARATOR, out);
fputs(_("Scheduling options:\n"), out);
fputs(_(" -R, --reset-on-fork set SCHED_RESET_ON_FORK for FIFO or RR\n"), out);
fputs(_(" -R, --reset-on-fork set reset-on-fork flag\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);
@ -173,22 +173,19 @@ static void __attribute__((__noreturn__)) usage(void)
static const char *get_policy_name(int policy)
{
#ifdef SCHED_RESET_ON_FORK
policy &= ~SCHED_RESET_ON_FORK;
#endif
switch (policy) {
case SCHED_OTHER:
return "SCHED_OTHER";
case SCHED_FIFO:
#ifdef SCHED_RESET_ON_FORK
case SCHED_FIFO | SCHED_RESET_ON_FORK:
#endif
return "SCHED_FIFO";
#ifdef SCHED_IDLE
case SCHED_IDLE:
return "SCHED_IDLE";
#endif
case SCHED_RR:
#ifdef SCHED_RESET_ON_FORK
case SCHED_RR | SCHED_RESET_ON_FORK:
#endif
return "SCHED_RR";
#ifdef SCHED_BATCH
case SCHED_BATCH:
@ -257,7 +254,7 @@ fallback:
else
prio = sp.sched_priority;
# ifdef SCHED_RESET_ON_FORK
if (policy == (SCHED_FIFO|SCHED_RESET_ON_FORK) || policy == (SCHED_BATCH|SCHED_RESET_ON_FORK))
if (policy & SCHED_RESET_ON_FORK)
reset_on_fork = 1;
# endif
}
@ -524,11 +521,6 @@ int main(int argc, char **argv)
errno = 0;
ctl->priority = strtos32_or_err(argv[optind], _("invalid priority argument"));
#ifdef SCHED_RESET_ON_FORK
if (ctl->reset_on_fork && ctl->policy != SCHED_FIFO && ctl->policy != SCHED_RR)
errx(EXIT_FAILURE, _("--reset-on-fork option is supported for "
"SCHED_FIFO and SCHED_RR policies only"));
#endif
#ifdef SCHED_DEADLINE
if ((ctl->runtime || ctl->deadline || ctl->period) && ctl->policy != SCHED_DEADLINE)
errx(EXIT_FAILURE, _("--sched-{runtime,deadline,period} options "