Re: [PATCH V3]hrtimer: Fix a performance regression by disable reprogramming in remove_hrtimer

[Peter Zijlstra]

On Mon, Sep 09, 2013 at 03:30:44PM +0200, Peter Zijlstra wrote:
> diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
> index fa6964d..486c0ba 100644
> --- a/drivers/idle/intel_idle.c
> +++ b/drivers/idle/intel_idle.c
> @@ -359,6 +359,14 @@ static int intel_idle(struct cpuidle_device *dev,
>       if (!(lapic_timer_reliable_states & (1 << (cstate))))
>               clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu);
>  
> +     current_thread_into()->status |= TS_POLLING;
> +
> +     /*
> +      * Order against setting of TS_POLLING against the reading of
> +      * NEED_RESCHED, matched by resched_task().
> +      */
> +     smp_mb();
> +
>       if (!need_resched()) {
>  
>               __monitor((void *)&current_thread_info()->flags, 0, 0);
> @@ -367,6 +375,8 @@ static int intel_idle(struct cpuidle_device *dev,
>                       __mwait(eax, ecx);
>       }
>  
> +     current_thread_into()->status &= ~TS_POLLING;
> +
>       if (!(lapic_timer_reliable_states & (1 << (cstate))))
>               clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu);

Hmm, arguably it would be better to set this from
intel_idle_cpuidle_driver_init() and clear it whenever this goes away.
Not sure how all that works, the cpuidle driver framework seems 'weird'.

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