MIME-Version: 1.0
In-Reply-To: <20120504120455.GB4413@somewhere.redhat.com>
References: <1336056962-10465-1-git-send-email-gilad@benyossef.com>
	<1336056962-10465-2-git-send-email-gilad@benyossef.com>
	<20120504120455.GB4413@somewhere.redhat.com>
Date: Fri, 4 May 2012 14:20:16 +0200
Message-ID: <CAFTL4hzSPbtTbL8gHy2SEnBv3rqWdk2UQL0uBUedqm2mmpHKiQ@mail.gmail.com>
Subject: Re: [PATCH v1 1/6] timer: make __next_timer_interrupt explicit about
 no future event
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Gilad Ben-Yossef <gilad@benyossef.com>,
        Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org, Tejun Heo <tj@kernel.org>,
        John Stultz <johnstul@us.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Mel Gorman <mel@csn.ul.ie>, Mike Frysinger <vapier@gentoo.org>,
        David Rientjes <rientjes@google.com>, Hugh Dickins <hughd@google.com>,
        Minchan Kim <minchan.kim@gmail.com>,
        Konstantin Khlebnikov <khlebnikov@openvz.org>,
        Christoph Lameter <cl@linux.com>, Chris Metcalf <cmetcalf@tilera.com>,
        Hakan Akkan <hakanakkan@gmail.com>,
        Max Krasnyansky <maxk@qualcomm.com>, linux-mm@kvack.org
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8BIT
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1441
Lines: 31

2012/5/4 Frederic Weisbecker <fweisbec@gmail.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@gmail.com>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/