[PATCH] sched: Reset bandwith on task when switching from SCHED_DEADLINE away

From: Daniel Wagner
Date: Wed Sep 03 2014 - 08:36:52 EST

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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@xxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
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@xxxxxxxx>, 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;

--
1.9.3

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Next message: Marc Zyngier: "Re: [PATCH v2 00/26] genirq: fix use of irq_find_mapping outside of legal RCU context"
Previous message: Lee Jones: "Re: [PATCH] x86, lpc, Allow only one load of lpc_ich"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]