Messages in this thread Patch in this message | | | Date | Mon, 12 May 2014 22:50:34 +0200 | From | Peter Zijlstra <> | Subject | Re: SCHED_DEADLINE, sched_getscheduler(), and sched_getparam() |
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On Mon, May 12, 2014 at 09:42:44PM +0200, Michael Kerrisk (man-pages) wrote: > > Hmm,.. maybe. Can we still change this? Again, maybe, there's not really > > that much userspace that relies on this. > > I think the sched_getparam() change is worthwhile (and the patches > could (should?) be marked for -stable). I suspect there's no user > space that relies on the current SCHED_DEADLINE behavior, and it's > worth avoiding the above breakage for sched_getparam(). I'd be > inclined to leave sched_getscheduler() as is: there's arguments > either way for how it should behave. > > > In any case, the way I read the little there is on getparam() it seems > > to imply the only case where it does make sense to call it at all is > > when sched_getscheduler() returns either SCHED_FIFO or SCHED_RR. > > (Yes, that's my understanding too.)
Something like so then, it encodes that reading explicitly.
--- Subject: sched: Change sched_getparam() behaviour vs SCHED_DEADLINE From: Peter Zijlstra <peterz@infradead.org> Date: Mon May 12 22:22:47 CEST 2014
The way we read POSIX one should only call sched_getparam() when sched_getscheduler() returns either SCHED_FIFO or SCHED_RR.
Given that we currently return sched_param::sched_priority=0 for all others, extend the same behaviour to SCHED_DEADLINE.
Requested-by: Michael Kerrisk <mtk.manpages@gmail.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> --- kernel/sched/core.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-)
Index: linux-2.6/kernel/sched/core.c =================================================================== --- linux-2.6.orig/kernel/sched/core.c +++ linux-2.6/kernel/sched/core.c @@ -3759,7 +3759,7 @@ SYSCALL_DEFINE1(sched_getscheduler, pid_ */ SYSCALL_DEFINE2(sched_getparam, pid_t, pid, struct sched_param __user *, param) { - struct sched_param lp; + struct sched_param lp = { .sched_priority = 0 }; struct task_struct *p; int retval; @@ -3776,11 +3776,8 @@ SYSCALL_DEFINE2(sched_getparam, pid_t, p if (retval) goto out_unlock; - if (task_has_dl_policy(p)) { - retval = -EINVAL; - goto out_unlock; - } - lp.sched_priority = p->rt_priority; + if (task_has_rt_policy(p)) + lp.sched_priority = p->rt_priority; rcu_read_unlock(); /*
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