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SubjectRe: 2.6.25-rc5-git6: Reported regressions from 2.6.24
Thomas Gleixner wrote:
> On Sat, 22 Mar 2008, Thomas Gleixner wrote:
>> On Sat, 22 Mar 2008, Gabriel C wrote:
>>> With this one TSC is fine but now I get a warning on boot :
>> Good. It confirms my assumptions about the root cause.
>>
>>> [ 0.041037] ------------[ cut here ]------------
>>> [ 0.041052] WARNING: at arch/x86/kernel/smp_32.c:562 native_smp_call_function_mask+0x23/0x11e()
>> Grr. I'll work out a solution for that one.
>
> Gabriel,
>
> I'm happy to rack your nerves some more.

No worries :)

>
> After discussing the issue with Peter and Ingo the following solution
> seems to be the one which is the least intrusive.
>
> Can you please give it a test ride ?

Done , git head + Andi's patch + this version of your patch does work here.

Also time-warp-test is just fine and everything else seems to work.


> ---
> include/linux/sched.h | 6 ++++++
> kernel/sched.c | 42 ++++++++++++++++++++++++++++++++++++++++++
> kernel/timer.c | 10 +++++++++-
> 3 files changed, 57 insertions(+), 1 deletion(-)
>
> Index: linux-2.6/include/linux/sched.h
> ===================================================================
> --- linux-2.6.orig/include/linux/sched.h
> +++ linux-2.6/include/linux/sched.h
> @@ -1541,6 +1541,12 @@ static inline void idle_task_exit(void)
>
> extern void sched_idle_next(void);
>
> +#ifdef CONFIG_NO_HZ
> +extern void wake_up_idle_cpu(int cpu);
> +#else
> +static inline void wake_up_idle_cpu(int cpu) { }
> +#endif
> +
> #ifdef CONFIG_SCHED_DEBUG
> extern unsigned int sysctl_sched_latency;
> extern unsigned int sysctl_sched_min_granularity;
> Index: linux-2.6/kernel/sched.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched.c
> +++ linux-2.6/kernel/sched.c
> @@ -848,6 +848,48 @@ static inline void resched_task(struct t
> __resched_task(p, TIF_NEED_RESCHED);
> }
>
> +#ifdef CONFIG_NO_HZ
> +/*
> + * When add_timer_on() enqueues a timer into the timer wheel of an
> + * idle CPU then this timer might expire before the next timer event
> + * which is scheduled to wake up that CPU. In case of a completely
> + * idle system the next event might even be infinite time into the
> + * future. wake_up_idle_cpu() ensures that the CPU is woken up and
> + * leaves the inner idle loop so the newle added timer is taken into
> + * account when the CPU goes back to idle and evaluates the timer
> + * wheel for the next timer event.
> + */
> +void wake_up_idle_cpu(int cpu)
> +{
> + struct rq *rq = cpu_rq(cpu);
> +
> + if (cpu == smp_processor_id())
> + return;
> +
> + /*
> + * This is safe, as this function is called with the timer
> + * wheel base lock of (cpu) held. When the CPU is on the way
> + * to idle and has not yet set rq->curr to idle then it will
> + * be serialized on the timer wheel base lock and take the new
> + * timer into account automatically.
> + */
> + if (rq->curr != rq->idle)
> + return;
> +
> + /*
> + * We can set TIF_RESCHED on the idle task of the other CPU
> + * lockless. The worst case is that the other CPU runs the
> + * idle task through an additional NOOP schedule()
> + */
> + set_tsk_thread_flag(rq->idle, TIF_NEED_RESCHED);
> +
> + /* NEED_RESCHED must be visible before we test polling */
> + smp_mb();
> + if (!tsk_is_polling(rq->idle))
> + smp_send_reschedule(cpu);
> +}
> +#endif
> +
> #ifdef CONFIG_SCHED_HRTICK
> /*
> * Use HR-timers to deliver accurate preemption points.
> Index: linux-2.6/kernel/timer.c
> ===================================================================
> --- linux-2.6.orig/kernel/timer.c
> +++ linux-2.6/kernel/timer.c
> @@ -451,10 +451,18 @@ void add_timer_on(struct timer_list *tim
> spin_lock_irqsave(&base->lock, flags);
> timer_set_base(timer, base);
> internal_add_timer(base, timer);
> + /*
> + * Check whether the other CPU is idle and needs to be
> + * triggered to reevaluate the timer wheel when nohz is
> + * active. We are protected against the other CPU fiddling
> + * with the timer by holding the timer base lock. This also
> + * makes sure that a CPU on the way to idle can not evaluate
> + * the timer wheel.
> + */
> + wake_up_idle_cpu(cpu);
> spin_unlock_irqrestore(&base->lock, flags);
> }
>
> -
> /**
> * mod_timer - modify a timer's timeout
> * @timer: the timer to be modified


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