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Subject: Re: [RFC][PATCH 17/22] sched: add signaling overrunning -deadline
 tasks.
From: Peter Zijlstra <peterz@infradead.org>
To: Raistlin <raistlin@linux.it>
Cc: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
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Date: Thu, 11 Nov 2010 22:58:21 +0100
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On Fri, 2010-10-29 at 08:40 +0200, Raistlin wrote:
> +static inline void __dl_signal(struct task_struct *tsk, int which)
> +{
> +       struct siginfo info;
> +       long long amount = which == SF_SIG_DMISS ? tsk->dl.stats.last_dmiss :
> +                          tsk->dl.stats.last_rorun;
> +
> +       info.si_signo = SIGXCPU;
> +       info.si_errno = which;
> +       info.si_code = SI_KERNEL;
> +       info.si_pid = 0;
> +       info.si_uid = 0;
> +       info.si_value.sival_int = (int)amount;
> +
> +       /* Correctly take the locks on task's sighand */
> +       __group_send_sig_info(SIGXCPU, &info, tsk);
> +       /* Log what happened to dmesg */
> +       printk(KERN_INFO "SCHED_DEADLINE: 0x%4x by %Ld [ns] in %d (%s)\n",
> +              which, amount, task_pid_nr(tsk), tsk->comm);
> +} 

This being a G-EDF like scheduler with a u<=1 schedulability test, we're
firmly in soft-rt territory which means the above will be very easy to
trigger.. Maybe not spam dmesg?