linux-kernel - Re: [rfc patch v2] rt,nohz_full: fix nohz_full for PREEMPT_RT

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Message-ID: <1428759368.10417.25.camel@gmail.com>
Date:	Sat, 11 Apr 2015 15:36:08 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	linux-rt-users <linux-rt-users@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>, rostedt@...dmis.org,
	John Kacur <jkacur@...hat.com>
Subject: Re: [rfc patch v2] rt,nohz_full: fix nohz_full for PREEMPT_RT_FULL

On Sat, 2015-04-11 at 15:15 +0200, Mike Galbraith wrote:
> 
> @@ -117,10 +113,8 @@ bool irq_work_queue(struct irq_work *wor
>         if (work->flags & IRQ_WORK_HARD_IRQ) {
>                 if (llist_add(&work->llnode, 
> this_cpu_ptr(&hirq_work_list)))
>                         arch_irq_work_raise();
> -       } else {
> -               if (llist_add(&work->llnode, 
> this_cpu_ptr(&lazy_list)))
> -                       arch_irq_work_raise();
> -       }
> +       } /* for lazy_list we have the timer irq */
> 
> If we don't queue work without IRQ_WORK_HARD_IRQ set, how does it 
> run?
> 
> Anyway, box did not livelock, nor did it with that bit reverted.

Well, not reverted, I actually queued and maybe poked softirq, but 
didn't check whether anything was being queued or not, only caring for 
the nonce whether box went catatonic or kept on working.

@@ -118,8 +115,9 @@ bool irq_work_queue(struct irq_work *wor
                if (llist_add(&work->llnode, this_cpu_ptr(&hirq_work_list)))
                        arch_irq_work_raise();
        } else {
-               if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)))
-                       arch_irq_work_raise();
+               if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) &&
+                   tick_nohz_tick_stopped())
+                       raise_softirq(TIMER_SOFTIRQ);


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