Messages in this thread | | | Date | Mon, 08 Sep 2014 16:13:54 +0100 | From | Juri Lelli <> | Subject | Re: [PATCH] sched: Reset bandwith on task when switching from SCHED_DEADLINE away |
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Hi Daniel,
thanks a lot for your patch. I'd actually have a slightly different fix for the same problem. I'm actually baking a small patchset that I should be able to release in the next few days. I'd say we could wait for that to happen and then discuss which approach is better, ok?
Thanks again,
- Juri
On 03/09/14 13:29, Daniel Wagner wrote: > Withouth reseting dl_bw the effect is any *new* task to switch > SCHED_DEADLINE will be prevented. You will get EBUSY for new tasks. > > sched_setattr() > if (... dl_overflow(p, policy, attr) ...) > __setscheduler() > __setscheduler_params() > __setparam_dl() > > sched_setattr() verifies if there is enough bandwith available before allowing > to switch to SCHED_DEALINE. Because we do not set p->dl.dl_bw back to 0 after > switching from SCHED_DEADLINE to any other scheduler we end up in dl_overflow() > to underflow the total bandwith (dl_b->total_bw). This can be triggered by > toggling between SCHED_DEADLINE and SCHED_OTHER. > > kernel/sched/core.c: > @@ -2039,8 +2039,12 @@ static int dl_overflow(struct task_struct *p, int policy, > u64 new_bw = dl_policy(policy) ? to_ratio(period, runtime) : 0; > int cpus, err = -1; > > - if (new_bw == p->dl.dl_bw) > + printk("dl_b->bw %llu dl_b->total_bw %llu p->dl.dl_bw %llu period %llu runtime %llu new_bw %llu -> ", > + dl_b->bw, dl_b->total_bw, p->dl.dl_bw, period, runtime, new_bw); > + > + if (new_bw == p->dl.dl_bw) { > + printk("1\n"); > return 0; > + } > > /* > * Either if a task, enters, leave, or stays -deadline but changes > @@ -2053,14 +2057,17 @@ static int dl_overflow(struct task_struct *p, int policy, > !__dl_overflow(dl_b, cpus, 0, new_bw)) { > __dl_add(dl_b, new_bw); > err = 0; > + printk("2\n"); > } else if (dl_policy(policy) && task_has_dl_policy(p) && > !__dl_overflow(dl_b, cpus, p->dl.dl_bw, new_bw)) { > __dl_clear(dl_b, p->dl.dl_bw); > __dl_add(dl_b, new_bw); > err = 0; > + printk("3\n"); > } else if (!dl_policy(policy) && task_has_dl_policy(p)) { > __dl_clear(dl_b, p->dl.dl_bw); > err = 0; > + printk("4\n"); > } > raw_spin_unlock(&dl_b->lock); > > [ 19.506909] dl_b->bw 996147 dl_b->total_bw 0 p->dl.dl_bw 0 period 200000 runtime 100000 new_bw 524288 -> 2 > [ 19.507906] dl_b->bw 996147 dl_b->total_bw 524288 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > [ 19.508906] dl_b->bw 996147 dl_b->total_bw 0 p->dl.dl_bw 524288 period 200000 runtime 100000 new_bw 524288 -> 1 > [ 19.509908] dl_b->bw 996147 dl_b->total_bw 0 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > [ 19.510993] dl_b->bw 996147 dl_b->total_bw 18446744073709027328 p->dl.dl_bw 524288 period 200000 runtime 100000 new_bw 524288 -> 1 > [ 19.513583] dl_b->bw 996147 dl_b->total_bw 18446744073709027328 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > [ 19.515686] dl_b->bw 996147 dl_b->total_bw 18446744073708503040 p->dl.dl_bw 524288 period 200000 runtime 100000 new_bw 524288 -> 1 > [ 19.517532] dl_b->bw 996147 dl_b->total_bw 18446744073708503040 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > [ 19.518503] dl_b->bw 996147 dl_b->total_bw 18446744073707978752 p->dl.dl_bw 524288 period 200000 runtime 100000 new_bw 524288 -> 1 > [ 19.519231] dl_b->bw 996147 dl_b->total_bw 18446744073707978752 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > [ 19.520027] dl_b->bw 996147 dl_b->total_bw 18446744073707454464 p->dl.dl_bw 524288 period 200000 runtime 100000 new_bw 524288 -> 1 > [ 19.520759] dl_b->bw 996147 dl_b->total_bw 18446744073707454464 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > [ 19.521460] dl_b->bw 996147 dl_b->total_bw 18446744073706930176 p->dl.dl_bw 524288 period 200000 runtime 100000 new_bw 524288 -> 1 > [ 19.522154] dl_b->bw 996147 dl_b->total_bw 18446744073706930176 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > [ 19.522809] dl_b->bw 996147 dl_b->total_bw 18446744073706405888 p->dl.dl_bw 524288 period 200000 runtime 100000 new_bw 524288 -> 1 > [ 19.523729] dl_b->bw 996147 dl_b->total_bw 18446744073706405888 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > [ 19.524569] dl_b->bw 996147 dl_b->total_bw 18446744073705881600 p->dl.dl_bw 524288 period 200000 runtime 100000 new_bw 524288 -> 1 > [ 19.525434] dl_b->bw 996147 dl_b->total_bw 18446744073705881600 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > [ 19.526224] dl_b->bw 996147 dl_b->total_bw 18446744073705357312 p->dl.dl_bw 524288 period 200000 runtime 100000 new_bw 524288 -> 1 > [ 19.527077] dl_b->bw 996147 dl_b->total_bw 18446744073705357312 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > > With the patch applied I get this result: > > [ 17.345812] dl_b->bw 996147 dl_b->total_bw 0 p->dl.dl_bw 0 period 200000 runtime 100000 new_bw 524288 -> 2 > [ 17.346664] dl_b->bw 996147 dl_b->total_bw 524288 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > [ 17.347333] dl_b->bw 996147 dl_b->total_bw 0 p->dl.dl_bw 0 period 200000 runtime 100000 new_bw 524288 -> 2 > [ 17.347832] dl_b->bw 996147 dl_b->total_bw 524288 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > [ 17.348369] dl_b->bw 996147 dl_b->total_bw 0 p->dl.dl_bw 0 period 200000 runtime 100000 new_bw 524288 -> 2 > [ 17.348868] dl_b->bw 996147 dl_b->total_bw 524288 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > [ 17.349456] dl_b->bw 996147 dl_b->total_bw 0 p->dl.dl_bw 0 period 200000 runtime 100000 new_bw 524288 -> 2 > [ 17.349953] dl_b->bw 996147 dl_b->total_bw 524288 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > [ 17.350598] dl_b->bw 996147 dl_b->total_bw 0 p->dl.dl_bw 0 period 200000 runtime 100000 new_bw 524288 -> 2 > [ 17.351107] dl_b->bw 996147 dl_b->total_bw 524288 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > [ 17.351637] dl_b->bw 996147 dl_b->total_bw 0 p->dl.dl_bw 0 period 200000 runtime 100000 new_bw 524288 -> 2 > [ 17.352144] dl_b->bw 996147 dl_b->total_bw 524288 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > [ 17.352805] dl_b->bw 996147 dl_b->total_bw 0 p->dl.dl_bw 0 period 200000 runtime 100000 new_bw 524288 -> 2 > [ 17.353366] dl_b->bw 996147 dl_b->total_bw 524288 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > [ 17.353867] dl_b->bw 996147 dl_b->total_bw 0 p->dl.dl_bw 0 period 200000 runtime 100000 new_bw 524288 -> 2 > [ 17.354458] dl_b->bw 996147 dl_b->total_bw 524288 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > [ 17.355066] dl_b->bw 996147 dl_b->total_bw 0 p->dl.dl_bw 0 period 200000 runtime 100000 new_bw 524288 -> 2 > [ 17.355716] dl_b->bw 996147 dl_b->total_bw 524288 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > [ 17.356414] dl_b->bw 996147 dl_b->total_bw 0 p->dl.dl_bw 0 period 200000 runtime 100000 new_bw 524288 -> 2 > [ 17.356961] dl_b->bw 996147 dl_b->total_bw 524288 p->dl.dl_bw 524288 period 0 runtime 0 new_bw 0 -> 4 > > Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: linux-kernel@vger.kernel.org > --- > This patch is based on mainline 3.17-rc3 > > And here my simple test program which triggers the problem. > Run it twice on your machine to see the error. > > /* > * Switch between SCHED_OTHER and SCHED_DEADLINE test. > * > * Parts stolen from libdl > * (C) Dario Faggioli <raistlin@linux.it>, 2009, 2010 > * > * This program is free software; you can redistribute it and/or modify > * it under the terms of the GNU General Public License as published by > * the Free Software Foundation version 2 of the License. > * > * This program is distributed in the hope that it will be useful, > * but WITHOUT ANY WARRANTY; without even the implied warranty of > * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > * GNU General Public License (COPYING file) for more details. > */ > > struct sched_attr { > __u32 size; > > __u32 sched_policy; > __u64 sched_flags; > > /* SCHED_NORMAL, SCHED_BATCH */ > __s32 sched_nice; > > /* SCHED_FIFO, SCHED_RR */ > __u32 sched_priority; > > /* SCHED_DEADLINE */ > __u64 sched_runtime; > __u64 sched_deadline; > __u64 sched_period; > }; > > static int sched_setattr(pid_t pid, const struct sched_attr *attr, > unsigned int flags) > { > return syscall(__NR_sched_setattr, pid, attr, flags); > } > > static void handle_err(const char *str) > { > perror(str); > exit(EXIT_FAILURE); > } > > int main(int argc, char *argv[]) > { > struct sched_attr other; > struct sched_attr dl; > int i, err; > > dl.size = sizeof(struct sched_attr); > dl.sched_policy = SCHED_DEADLINE; > dl.sched_flags = 0; > dl.sched_nice = 0; > dl.sched_priority = 0; > dl.sched_runtime = 100000; > dl.sched_deadline = 200000; > dl.sched_period = 200000; > > other.size = sizeof(struct sched_attr); > other.sched_policy = SCHED_OTHER; > other.sched_flags = 0; > other.sched_nice = 0; > other.sched_priority = 0; > other.sched_runtime = 0; > other.sched_deadline = 0; > other.sched_period = 0; > > for (i = 0; i < 10; i++) { > err = sched_setattr(0, &dl, 0); > if (err < 0) > handle_err("Could not set SCHED_DEADLINE attributes"); > > err = sched_setattr(0, &other, 0); > if (err < 0) > handle_err("Could not set SCHED_OTHER attributes"); > } > > return 0; > } > --- > kernel/sched/core.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index ec1a286..1ce935e 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3236,6 +3236,9 @@ static void __setscheduler_params(struct task_struct *p, > { > int policy = attr->sched_policy; > > + if (!dl_policy(policy) && task_has_dl_policy(p)) > + p->dl.dl_bw = 0; > + > if (policy == SETPARAM_POLICY) > policy = p->policy; > >
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