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Message-ID: <540DC7B2.6000000@arm.com>
Date: Mon, 08 Sep 2014 16:13:54 +0100
From: Juri Lelli <juri.lelli@....com>
To: Daniel Wagner <daniel.wagner@...-carit.de>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>
CC: "juri.lelli@...il.com" <juri.lelli@...il.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: Reset bandwith on task when switching from SCHED_DEADLINE
away
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@...-carit.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: linux-kernel@...r.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@...ux.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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