linux-kernel - Re: [BUG] [ tip/sched/core ] System unresponsive after booting

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Message-ID: <20140115113015.GB31570@twins.programming.kicks-ass.net>
Date:	Wed, 15 Jan 2014 12:30:15 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Michael wang <wangyun@...ux.vnet.ibm.com>
Cc:	Daniel Lezcano <daniel.lezcano@...aro.org>, raistlin@...ux.it,
	juri.lelli@...il.com, Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] [ tip/sched/core ] System unresponsive after booting

On Wed, Jan 15, 2014 at 05:25:55PM +0800, Michael wang wrote:
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 0326c06..bf4a6ed 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3464,6 +3464,10 @@ int sched_setscheduler(struct task_struct *p, int
> policy,
>                 .sched_policy   = policy,
>                 .sched_priority = param->sched_priority
>         };
> +
> +       if (fair_policy(policy))
> +               attr.sched_nice = PRIO_TO_NICE(attr.sched_priority);
> +
>         return __sched_setscheduler(p, &attr, true);
>  }
>  EXPORT_SYMBOL_GPL(sched_setscheduler);
> @@ -3494,6 +3498,10 @@ int sched_setscheduler_nocheck(struct task_struct
> *p, int policy,
>                 .sched_policy   = policy,
>                 .sched_priority = param->sched_priority
>         };
> +
> +       if (fair_policy(policy))
> +               attr.sched_nice = PRIO_TO_NICE(attr.sched_priority);
> +
>         return __sched_setscheduler(p, &attr, false);
>  }

That seems wrong; the manpage confirms, from sched_setscheduler(2):

       For processes scheduled under one of the normal scheduling
       policies (SCHED_OTHER, SCHED_IDLE, SCHED_BATCH), sched_priority
       is not used in scheduling decisions (it must  be  speci‐ fied as
       0).

That said; we should probably preserve the nice value, which with the
current code we reset to 0.

---
 kernel/sched/core.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0326c06953eb..f3abbb7dae62 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3462,7 +3462,8 @@ int sched_setscheduler(struct task_struct *p, int policy,
 {
 	struct sched_attr attr = {
 		.sched_policy   = policy,
-		.sched_priority = param->sched_priority
+		.sched_priority = param->sched_priority,
+		.sched_nice	= PRIO_TO_NICE(p->static_prio),
 	};
 	return __sched_setscheduler(p, &attr, true);
 }
@@ -3492,7 +3493,8 @@ int sched_setscheduler_nocheck(struct task_struct *p, int policy,
 {
 	struct sched_attr attr = {
 		.sched_policy   = policy,
-		.sched_priority = param->sched_priority
+		.sched_priority = param->sched_priority,
+		.sched_nice	= PRIO_TO_NICE(p->static_prio),
 	};
 	return __sched_setscheduler(p, &attr, false);
 }
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