[lkml]   [2011]   [Mar]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH] sched: leave sched_setscheduler earlier if possible.
sched_setscheduler (in sched.c) is called in order of changing the
scheduling policy and/or the real-time priority of a task. Thus,
if we find out that neither of those are actually being modified, it
is possible to return earlier and save the overhead of a full
deactivate+activate cycle of the task in question.

Beside that, if we have more than one SCHED_FIFO task with the same
priority on the same rq (which means they share the same priority queue)
having one of them changing its position in the priority queue because of
a sched_setscheduler (as it happens by means of the deactivate+activate)
that does not actually change the priority violates POSIX which states,

"If a thread whose policy or priority has been modified by
pthread_setschedprio() is a running thread or is runnable, the effect on
its position in the thread list depends on the direction of the
modification, as follows: a. <...> b. If the priority is unchanged, the
thread does not change position in the thread list. c. <...>"


Signed-off-by: Dario Faggioli <>
kernel/sched.c | 10 ++++++++++
1 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index c5ae6bc..d73bbc5 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4998,6 +4998,16 @@ recheck:
return -EINVAL;

+ /*
+ * If not changing anything there's no need to proceed further
+ */
+ if (unlikely(policy == p->policy && (!rt_policy(policy) ||
+ param->sched_priority == p->rt_priority))) {
+ __task_rq_unlock(rq);
+ raw_spin_unlock_irqrestore(&p->pi_lock, flags);
+ return 0;
+ }
if (user) {
<<This happens because I choose it to happen!>> (Raistlin Majere)
Dario Faggioli, ReTiS Lab, Scuola Superiore Sant'Anna, Pisa (Italy) --

[unhandled content-type:application/pgp-signature]
 \ /
  Last update: 2011-03-24 15:03    [W:0.059 / U:0.084 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site