linux-kernel - Re: [PATCH v1 1/6] timer: make __next_timer_interrupt explicit about no future event

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Message-ID: <CAFTL4hzSPbtTbL8gHy2SEnBv3rqWdk2UQL0uBUedqm2mmpHKiQ@mail.gmail.com>
Date:	Fri, 4 May 2012 14:20:16 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Gilad Ben-Yossef <gilad@...yossef.com>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	John Stultz <johnstul@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>, Mike Frysinger <vapier@...too.org>,
	David Rientjes <rientjes@...gle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Christoph Lameter <cl@...ux.com>,
	Chris Metcalf <cmetcalf@...era.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Max Krasnyansky <maxk@...lcomm.com>, linux-mm@...ck.org
Subject: Re: [PATCH v1 1/6] timer: make __next_timer_interrupt explicit about
 no future event

2012/5/4 Frederic Weisbecker <fweisbec@...il.com>:
> On Thu, May 03, 2012 at 05:55:57PM +0300, Gilad Ben-Yossef wrote:
>> @@ -1317,9 +1322,15 @@ unsigned long get_next_timer_interrupt(unsigned long now)
>>       if (cpu_is_offline(smp_processor_id()))
>>               return now + NEXT_TIMER_MAX_DELTA;
>>       spin_lock(&base->lock);
>> -     if (time_before_eq(base->next_timer, base->timer_jiffies))
>> -             base->next_timer = __next_timer_interrupt(base);
>> -     expires = base->next_timer;
>> +     if (time_before_eq(base->next_timer, base->timer_jiffies)) {
>> +
>> +             if (__next_timer_interrupt(base, &expires))
>> +                     base->next_timer = expires;
>> +             else
>> +                     expires = now + NEXT_TIMER_MAX_DELTA;
>
> I believe you can update base->next_timer to now + NEXT_TIMER_MAX_DELTA,
> so on any further idle interrupt exit that call tick_nohz_stop_sched_tick(),
> we won't get again the overhead of __next_timer_interrupt().

Ah forget that, I was confused. If we do that we actually get the useless timer
at now + NEXT_TIMER_MAX_DELTA.

So I think the patch is fine.

Acked-by: Frederic Weisbecker <fweisbec@...il.com>
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