From: Steven Rostedt <rostedt@goodmis.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>,
"Duetsch, Thomas LDE1" <thomas.duetsch@siemens.com>
Subject: [RT] rt priority losing
Date: Mon, 24 Jul 2006 11:41:00 -0400 [thread overview]
Message-ID: <1153755660.4002.137.camel@localhost.localdomain> (raw)
Ingo or Tglx,
It has come to my attention that the dynamic hrtimer softirq can lose a
boosted priority. That is, if a softirq is running while a timeout
happens, and the call back is of lower priority than the currently
running hrtimer softirq, the timer interrupt will still lower the
hrtimer softirq.
Here's the problem code:
static void wakeup_softirqd_prio(int softirq, int prio)
{
/* Interrupts are disabled: no need to stop preemption */
struct task_struct *tsk = __get_cpu_var(ksoftirqd[softirq].tsk);
if (tsk) {
if (tsk->normal_prio != prio) {
struct sched_param param;
param.sched_priority = MAX_RT_PRIO-1 - prio;
setscheduler(tsk, -1, SCHED_FIFO, ¶m);
}
if(tsk->state != TASK_RUNNING)
wake_up_process(tsk);
}
}
So, tsk could be softirqd-hrmono and we lower the priority. (only
normal_prio is checked versus prio).
So this can be a problem, if the softirq function holds a lock of a high
priority task, and is running boosted. If another timer goes off with a
lower priority, we can lower the priority of the softirqd and lose the
inherited priority that it was running at.
-- Steve
next reply other threads:[~2006-07-24 15:41 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-07-24 15:41 Steven Rostedt [this message]
2006-07-24 17:00 ` [RT] rt priority losing Esben Nielsen
2006-07-24 16:37 ` Steven Rostedt
2006-07-24 16:44 ` Thomas Gleixner
2006-07-24 17:54 ` Esben Nielsen
2006-07-24 17:15 ` [PATCH -rt] Don't let raise_softirq_prio lower the prio (was: [RT] rt priority losing) Steven Rostedt
2006-07-26 8:10 ` Ingo Molnar
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