Date: Tue, 15 Apr 2014 10:48:54 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Cc: linux-kernel@vger.kernel.org,
        Fernando Luis Vazquez Cao <fernando_b1@lab.ntt.co.jp>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Preeti U Murthy <preeti@linux.vnet.ibm.com>,
        Denys Vlasenko <vda.linux@googlemail.com>, stable@vger.kernel.org
Subject: Re: [PATCH 1/2] nohz: stop updating sleep stats from
 get_cpu_{idle,iowait}_time_us()
Message-ID: <20140415084854.GL11096@twins.programming.kicks-ass.net>
References: <53465F54.708@jp.fujitsu.com>
 <53466027.3040705@jp.fujitsu.com>
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On Thu, Apr 10, 2014 at 06:11:03PM +0900, Hidetoshi Seto wrote:
> -	if (ts->idle_active) {
> -		delta = ktime_sub(now, ts->idle_entrytime);
> -		if (nr_iowait_cpu(cpu) > 0)
> -			ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
> -		else
> -			ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
> -		ts->idle_entrytime = now;
> -	}
> -
> -	if (last_update_time)
> -		*last_update_time = ktime_to_us(now);
> -
> -}
> -
> -static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
> -{
> -	update_ts_time_stats(smp_processor_id(), ts, now, NULL);
> +	/* Updates the per cpu time idle statistics counters */
> +	delta = ktime_sub(now, ts->idle_entrytime);
> +	if (nr_iowait_cpu(smp_processor_id()) > 0)

Now I know the old code also uses nr_iowait_cpu(), but that function is
crackbrained. This cannot possibly be right.

Anything using nr_iowait_cpu() is broken beyond repair.
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