From: Frederic Weisbecker <fweisbec@gmail.com>
To: Byungchul Park <byungchul.park@lge.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
Chris Metcalf <cmetcalf@ezchip.com>,
Thomas Gleixner <tglx@linutronix.de>,
Luiz Capitulino <lcapitulino@redhat.com>,
Christoph Lameter <cl@linux.com>,
"Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
Mike Galbraith <efault@gmx.de>, Rik van Riel <riel@redhat.com>,
Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH 2/3] sched: Correctly handle nohz ticks cpu load accounting
Date: Mon, 18 Apr 2016 15:35:06 +0200 [thread overview]
Message-ID: <20160418133504.GA29716@lerouge> (raw)
In-Reply-To: <20160418091721.GH2279@X58A-UD3R>
On Mon, Apr 18, 2016 at 06:17:21PM +0900, Byungchul Park wrote:
> On Wed, Apr 13, 2016 at 03:56:51PM +0200, Frederic Weisbecker wrote:
> > @@ -4645,11 +4674,11 @@ void cpu_load_update_nohz(int active)
> > void cpu_load_update_active(struct rq *this_rq)
> > {
> > unsigned long load = weighted_cpuload(cpu_of(this_rq));
> > - /*
> > - * See the mess around cpu_load_update_idle() / cpu_load_update_nohz().
> > - */
> > - this_rq->last_load_update_tick = jiffies;
> > - __cpu_load_update(this_rq, load, 1, 1);
> > +
> > + if (tick_nohz_tick_stopped())
> > + cpu_load_update_nohz(this_rq, READ_ONCE(jiffies), load);
> > + else
> > + cpu_load_update_periodic(this_rq, load);
>
> Considering it further, I wonder if needing it.
> (Sorry if I missed something.)
>
> Case 1. tickless -> (scheduler_tick) -> tickless
>
> I am not sure for this case if the rq's load can be changed or not,
> especially, if the rq's load can be changed *at this point*.
> Please remind that the load[0] is set here.
load[0] won't change because it's set by cpu_load_update_nohz_start().
But all the other load[idx] need to be decayed further.
>
> Case 2. tickless -> (scheduler_tick) -> restart tick
>
> Will be done by the tick restart routine when exiting irq.
> -> no problem.
>
> Case 3. tick -> (scheduler_tick) -> tickless
>
> Same as before.
> -> no problem.
>
> Case 4. tick -> (scheduler_tick) -> tick
>
> We can rely on regular schedule_tick().
> -> no problem.
>
Thanks for your review!
next prev parent reply other threads:[~2016-04-18 13:35 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-13 13:56 [PATCH 0/3] sched: Fix/improve nohz cpu load updates v3 Frederic Weisbecker
2016-04-13 13:56 ` [PATCH 1/3] sched: Gather cpu load functions under a more conventional namespace Frederic Weisbecker
2016-04-23 12:58 ` [tip:sched/core] sched/fair: Gather CPU " tip-bot for Frederic Weisbecker
2016-04-13 13:56 ` [PATCH 2/3] sched: Correctly handle nohz ticks cpu load accounting Frederic Weisbecker
2016-04-18 8:22 ` Byungchul Park
2016-04-18 9:17 ` Byungchul Park
2016-04-18 13:35 ` Frederic Weisbecker [this message]
2016-04-19 0:01 ` Byungchul Park
2016-04-19 14:01 ` Frederic Weisbecker
2016-04-20 7:59 ` Wanpeng Li
2016-04-23 12:59 ` [tip:sched/core] sched/fair: Correctly handle nohz ticks CPU " tip-bot for Frederic Weisbecker
2016-04-13 13:56 ` [PATCH 3/3] sched: Optimize !CONFIG_NO_HZ_COMMON cpu load updates Frederic Weisbecker
2016-04-18 13:36 ` Frederic Weisbecker
2016-04-19 15:36 ` [PATCH v2] " Frederic Weisbecker
2016-04-23 12:59 ` [tip:sched/core] sched/fair: Optimize !CONFIG_NO_HZ_COMMON CPU " tip-bot for Frederic Weisbecker
-- strict thread matches above, loose matches on Subject: below --
2016-04-08 1:07 [PATCH 0/3] sched: Fix/improve nohz cpu load updates v2 Frederic Weisbecker
2016-04-08 1:07 ` [PATCH 2/3] sched: Correctly handle nohz ticks cpu load accounting Frederic Weisbecker
2016-04-08 9:41 ` Peter Zijlstra
2016-04-08 12:53 ` Frederic Weisbecker
2016-04-08 17:40 ` Peter Zijlstra
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