6 Jun
2015
6 Jun
'15
11:11 p.m.
On Sat, Jun 06, 2015 at 03:35:16PM +0100, Harry van Haaren wrote:
On Sat, Apr 4, 2015 at 8:13 PM, Adrian Knoth
<adi(a)drcomp.erfurt.thur.de>
wrote:
No tested but perhaps the follow lines in __sched_setscheduler
(linux-3.19.8/kernel/sched/core.c) are relevant:
#ifdef CONFIG_RT_GROUP_SCHED
/*
* Do not allow realtime tasks into groups that have no runtime
* assigned.
*/
if (rt_bandwidth_enabled() && rt_policy(policy) &&
task_group(p)->rt_bandwidth.rt_runtime == 0 &&
!task_group_is_autogroup(task_group(p))) {
task_rq_unlock(rq, p, &flags);
return -EPERM;
}
#endif
#ifdef CONFIG_SMP
if (dl_bandwidth_enabled() && dl_policy(policy)) {
cpumask_t *span = rq->rd->span;
/*
* Don't allow tasks with an affinity mask smaller than
* the entire root_domain to become SCHED_DEADLINE. We
* will also fail if there's no bandwidth available.
*/
if (!cpumask_subset(span, &p->cpus_allowed) ||
rq->rd->dl_bw.bw == 0) {
task_rq_unlock(rq, p, &flags);
return -EPERM;
}
}
#endif
However I'm using 3.10 compiled without CONFIG_RT_GROUP_SCHED and the
second `#ifdef' (CONFIG_SMP) is not present in the source code.
Hypothesis: the second condition fails
=> disable the bandwidth management logic (the default is 950000):
echo -1 > /proc/sys/kernel/sched_rt_runtime_us
More info about sched_rt_runtime_us:
scheduler/sched-rt-group.txt: "2.1 System wide settings"
scheduler/sched-deadline.txt: "4.1 System wide settings"
If it continues to fail and your kernel is compiled with
CONFIG_RT_GROUP_SCHED, you could recompile it without this
configuration option (if you don't use realtime group scheduling).
Oh, if it continues to fail, see the other branches with `return -EPERM'
in __sched_setscheduler.
Not enough information. I recommend starting
jackd with strace
Done - apologies for the delay. Strace output available[1], but the most
interesting part copied here:
sched_get_priority_min(SCHED_FIFO) = 1
sched_setscheduler(0, SCHED_FIFO, { 1 }) = -1 EPERM (Operation not
permitted)
write(2, "\nJACK is running in realtime mod"..., 87
JACK is running in realtime mode, but you are not allowed to use realtime
scheduling.
) = 87
This code tries to call sched_setscheduler() with
SCHED_FIFO. My bet is
that your "almost vanilla kernel" fails to fulfil this request, but
strace will tell you for sure.
By "almost vanilla" I meant the Arch linux packaged version - I
didn't
change the config myself (and Arch aims to be true to vanilla). A very
accurace prediction though - indeed sched_setscheduler() is causing a
return of -1. This is running as root though - so something is wrong here.
The question is why said call should fail. The
only thing that comes to
my mind are CGROUPS. Maybe your old kernel comes without, the new kernel
supports them and the configuration is set in a way that disables
SCHED_FIFO by default.
Perhaps - I'm not experienced with cgroups or such, if anybody has any test
ideas for me I'll try them out?