linux-kernel - Re: [v5 PATCH 4/4] timers: logic to move non pinned timers

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Date:	Mon, 6 Apr 2009 18:48:48 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Arun R Bharadwaj <arun@...ux.vnet.ibm.com>
cc:	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org,
	a.p.zijlstra@...llo.nl, ego@...ibm.com, mingo@...e.hu,
	andi@...stfloor.org, venkatesh.pallipadi@...el.com,
	vatsa@...ux.vnet.ibm.com, arjan@...radead.org,
	svaidy@...ux.vnet.ibm.com
Subject: Re: [v5 PATCH 4/4] timers: logic to move non pinned timers

Arun,

On Mon, 6 Apr 2009, Arun R Bharadwaj wrote:
> +again:
> +	new_cpu_base = &per_cpu(hrtimer_bases, cpu);
>  	new_base = &new_cpu_base->clock_base[base->index];
>  
>  	if (base != new_base) {
> @@ -219,6 +230,34 @@ switch_hrtimer_base(struct hrtimer *time
>  		timer->base = NULL;
>  		spin_unlock(&base->cpu_base->lock);
>  		spin_lock(&new_base->cpu_base->lock);
> +
> +		if (cpu == preferred_cpu) {
> +			/* Calculate clock monotonic expiry time */
> +			ktime_t expires = ktime_sub(hrtimer_get_expires(timer),
> +							new_base->offset);
> +
> +			/*
> +			 * Get the next event on target cpu from the
> +			 * clock events layer.
> +			 * This covers the highres=off nohz=on case as well.
> +			 */
> +			ktime_t next = clockevents_get_next_event(cpu);
> +
> +			ktime_t delta = ktime_sub(expires, next);
> +
> +			/*
> +			 * We do not migrate the timer when it is expiring
> +			 * before the next event on the target cpu because
> +			 * we cannot reprogram the target cpu hardware and
> +			 * we would cause it to fire late.
> +			 */
> +			if (delta.tv64 < 0) {
> +				cpu = smp_processor_id();
> +				spin_unlock(&new_base->cpu_base->lock);
> +				spin_lock(&base->cpu_base->lock);

Darn, I knew that I missed something when I looked at this before:

      	     	    	   	 timer->base = base;

Thanks,

	tglx
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