linux-kernel - Re: [PATCH] avoid using smp_processor_id() in preemptible code (nr_iowait

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Date:	Tue, 15 Jun 2010 18:23:15 +0300
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Jiri Slaby <jslaby@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] avoid using smp_processor_id() in preemptible code
 (nr_iowait_cpu)

On (06/15/10 08:08), Arjan van de Ven wrote:
> On Tue, 15 Jun 2010 17:50:29 +0300
> Sergey Senozhatsky <sergey.senozhatsky@...il.com> wrote:
> > > 
> > > hmm this part is wrong
> > > you pick the current cpu, rather than the one denoted by ts.....
> > > 
> > 
> > Hmm. Thanks, good catch. 
> > Well, there is something I'm missing. How can I match given *ts and
> > cpu in update_ts_time_stats (except for introducing
> > update_ts_time_stats(..., int cpu)) ?
> 
> 
> that'd be option one

We'll have problem in tick_nohz_start_idle(struct tick_sched *ts)
{
	ktime_t now;
	now = ktime_get();
	update_ts_time_stats(ts, now, NULL);

...
So, we also will have to expand it to tick_nohz_start_idle(struct tick_sched *ts, int cpu)

That's why I prefer option #2.

> option two is to add a "cpu" member to struct tick_sched.....
> 
Thought about that. Seems ok to me.


> if you go for option one, I'd replace the ts argument with the cpu
> argument.....
> 
> 

Hmm, I missed this one (replacing *ts to int cpu). And I like it. 
Something like:

-update_ts_time_stats(struct tick_sched *ts, ktime_t now, u64 *last_update_time)
+update_ts_time_stats(int cpu, ktime_t now, u64 *last_update_time)
{
	ktime_t delta;
+	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);

	if (ts->idle_active) {
		int cpu = get_cpu();
		delta = ktime_sub(now, ts->idle_entrytime);
		ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
		if (nr_iowait_cpu(cpu) > 0)
			ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
		put_cpu();
		ts->idle_entrytime = now;
+		ts->idle_active = 0;
	}

	if (last_update_time)
		*last_update_time = ktime_to_us(now);

}


static void tick_nohz_stop_idle(int cpu, ktime_t now)
{
-	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);

	update_ts_time_stats(cpu, now, NULL);
-	ts->idle_active = 0;

	sched_clock_idle_wakeup_event(0);
}

and so on.


	Sergey

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