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Date: Wed, 30 Nov 2011 11:24:46 +0100 (CET)
From: Thomas Gleixner <tglx@...utronix.de>
To: Mike Galbraith <efault@....de>
cc: Steven Rostedt <rostedt@...dmis.org>,
LKML <linux-kernel@...r.kernel.org>,
RT <linux-rt-users@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
Clark Williams <williams@...hat.com>
Subject: Re: [PATCH RT] tasklet/rt: Prevent tasklets from going into infinite
spin in RT
On Wed, 30 Nov 2011, Mike Galbraith wrote:
> On Tue, 2011-11-29 at 20:55 -0500, Steven Rostedt wrote:
> > Ingo,
> >
> > I forward ported this code from 2.6.33.9-rt31, but I think you were the
> > original author, as I found most of this code in the
> > "tasklet-redesign.patch" from my broken out 2.6.24-rt patches. I
> > committed it into my git tree (stable-rt) under your name, and added the
> > Signed-off-by that you had in that patch, if you have and objections,
> > please let me know. This patch should never see mainline, but it will
> > probably be going into the -rt branch. I wrote up this change log, if
> > there's something you don't like in it, let me know and I'll fix it.
>
> I'm oh so happy to see this. I've been going nuts trying to figure out
> why the heck 33-rt doesn't go bonkers, but 30+ rt does.
>
> > Luis and Clark (I love saying that),
> >
> > I booted this patch against 3.0-rt stable, and it didn't crash ;)
> > Could you apply it and see if it fixes the hang that you've been seeing.
>
> I'll most certainly be testing it too. With the below, and the
> conditional yield thingy disabled, all I have to do is boot x3550 M3
> box, and it'll hang very frequently, but not always, with sirq-tasklet
> going stark raving mad. Yielding fix^Wmakes it not do the bad thing.
>
> (somewhat less disgusting version of sirq threads patch;)
>
> sched, rt: resurrect softirq threads for RT_FULL
>
> Signed-off-by: Mike Galbraith <efault@....de>
> ---
> include/linux/interrupt.h | 46 ++++++++++
> kernel/irq/Kconfig | 7 +
> kernel/sched.c | 4
> kernel/softirq.c | 194 ++++++++++++++++++++++++++++++++--------------
> 4 files changed, 191 insertions(+), 60 deletions(-)
>
> Index: linux-3.2-rt/kernel/irq/Kconfig
> ===================================================================
> --- linux-3.2-rt.orig/kernel/irq/Kconfig
> +++ linux-3.2-rt/kernel/irq/Kconfig
> @@ -60,6 +60,13 @@ config IRQ_DOMAIN
> config IRQ_FORCED_THREADING
> bool
>
> +# Support forced sirq threading
> +config SIRQ_FORCED_THREADING
> + bool "Forced Soft IRQ threading"
> + depends on PREEMPT_RT_FULL
> + help
> + Split ksoftirqd into per SOFTIRQ threads
> +
> config SPARSE_IRQ
> bool "Support sparse irq numbering"
> depends on HAVE_SPARSE_IRQ
> Index: linux-3.2-rt/include/linux/interrupt.h
> ===================================================================
> --- linux-3.2-rt.orig/include/linux/interrupt.h
> +++ linux-3.2-rt/include/linux/interrupt.h
> @@ -442,6 +442,9 @@ enum
> NR_SOFTIRQS
> };
>
> +/* Update when adding new softirqs. */
> +#define SOFTIRQ_MASK_ALL 0x3ff
> +
> /* map softirq index to softirq name. update 'softirq_to_name' in
> * kernel/softirq.c when adding a new softirq.
> */
> @@ -457,10 +460,16 @@ struct softirq_action
> };
>
> #ifndef CONFIG_PREEMPT_RT_FULL
> +#define NR_SOFTIRQ_THREADS 1
> asmlinkage void do_softirq(void);
> asmlinkage void __do_softirq(void);
> static inline void thread_do_softirq(void) { do_softirq(); }
> #else
> +#ifdef CONFIG_SIRQ_FORCED_THREADING
> +#define NR_SOFTIRQ_THREADS NR_SOFTIRQS
> +#else
> +#define NR_SOFTIRQ_THREADS 1
> +#endif
> extern void thread_do_softirq(void);
> #endif
>
> @@ -486,12 +495,43 @@ extern void softirq_check_pending_idle(v
> */
> DECLARE_PER_CPU(struct list_head [NR_SOFTIRQS], softirq_work_list);
>
> -DECLARE_PER_CPU(struct task_struct *, ksoftirqd);
> +struct softirqdata {
> + int mask;
> + struct task_struct *tsk;
> +};
> +
> +DECLARE_PER_CPU(struct softirqdata [NR_SOFTIRQ_THREADS], ksoftirqd);
> +
> +static inline bool this_cpu_ksoftirqd(struct task_struct *p)
> +{
> + int i;
> +
> + for (i = 0; i < NR_SOFTIRQ_THREADS; i++) {
> + if (p == __get_cpu_var(ksoftirqd)[i].tsk)
> + return true;
You are not serious about that loop, are you ?
> + }
>
> -static inline struct task_struct *this_cpu_ksoftirqd(void)
> + return false;
> +}
> +
> +#ifdef CONFIG_PREEMPT_RT_FULL
> +static inline int task_sirq_mask(struct task_struct *p)
> +{
> + int i;
> +
> + for (i = 0; i < NR_SOFTIRQ_THREADS; i++) {
> + if (p == __get_cpu_var(ksoftirqd)[i].tsk)
> + return __get_cpu_var(ksoftirqd)[i].mask;
Looks you are
> @@ -131,11 +155,18 @@ void softirq_check_pending_idle(void)
> */
> static void wakeup_softirqd(void)
> {
> - /* Interrupts are disabled: no need to stop preemption */
> - struct task_struct *tsk = __this_cpu_read(ksoftirqd);
> + struct task_struct *tsk;
> + u32 pending = local_softirq_pending(), mask, i;
>
> - if (tsk && tsk->state != TASK_RUNNING)
> - wake_up_process(tsk);
> + /* Interrupts are disabled: no need to stop preemption */
> + for (i = 0; pending && i < NR_SOFTIRQ_THREADS; i++) {
> + mask = __get_cpu_var(ksoftirqd)[i].mask;
> + if (!(pending & mask))
> + continue;
> + tsk = __get_cpu_var(ksoftirqd)[i].tsk;
> + if (tsk && tsk->state != TASK_RUNNING)
> + wake_up_process(tsk);
> + }
> }
Dammned serious is seems. :)
I was looking into that as well, though I did not want to inflict it
on 3.0 at this point.
Thanks,
tglx
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