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From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Doug Smythies <dsmythies@telus.net>,
	Thomas Ilsche <thomas.ilsche@tu-dresden.de>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Linux PM <linux-pm@vger.kernel.org>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Paul McKenney <paulmck@linux.vnet.ibm.com>,
	Rik van Riel <riel@surriel.com>,
	Aubrey Li <aubrey.li@linux.intel.com>,
	Mike Galbraith <mgalbraith@suse.de>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFT][PATCH v7 6/8] sched: idle: Select idle state before stopping the tick
Date: Thu, 29 Mar 2018 01:11:11 +0200
Message-ID: <CAJZ5v0g6=f60Owy2NLSeXZs7hL4tGECseqhwgy7h0imLOTvt5w@mail.gmail.com> (raw)
In-Reply-To: <006501d3c6d5$2d03e500$870baf00$@net>

On Wed, Mar 28, 2018 at 10:41 PM, Doug Smythies <dsmythies@telus.net> wrote:
> On 2018.03.28 08:15 Thomas Ilsche wrote:
>> On 2018-03-28 12:56, Rafael J. Wysocki wrote:
>>> On Wed, Mar 28, 2018 at 12:37 PM, Rafael J. Wysocki <rafael@kernel.org> wrote:
>>>> On Wed, Mar 28, 2018 at 10:38 AM, Thomas Ilsche
>>>> <thomas.ilsche@tu-dresden.de> wrote:
>>>>> On 2018-03-28 10:13, Rafael J. Wysocki wrote:
>>>>>>
>>>
>>> [cut]
>>>
>>>>
>>>> So I do
>>>>
>>>> $ for cpu in 0 1 2 3; do taskset -c $cpu sh -c 'while true; do usleep
>>>> 500; done' & done
>>>>
>>>> which is a shell kind of imitation of the above and I cannot see this
>>>> issue at all.
>>>>
>>>> I count the number of times data->next_timer_us in menu_select() is
>>>> greater than TICK_USEC and while this "workload" is running, that
>>>> number is exactly 0.
>>>>
>>>> I'll try with a C program still.
>>>
>>> And with a C program I see data->next_timer_us greater than TICK_USEC
>>> while it is running, so let me dig deeper.
>>>
>>
>> I can confirm that a shell-loop behaves differently like you describe.
>> Even if it's just a shell-loop calling "main{usleep(500);}" binary.
>
> I normally use the C program method.
> The timer there returns with the need_sched() flag set.

I found the problem, but addressing it will not be straightforward,
which is kind of unfortunate.

Namely, get_next_timer_interrupt() doesn't take high resolution timers
into account if they are enabled (which I overlooked), but they
obviously need to be taken into account in
tick_nohz_get_sleep_length(), so calling tick_nohz_next_event() in
there is not sufficient.

Moreover, it needs to know the next highres timer not including the
tick and that's not so easy to get.  It is doable, though, AFAICS.

  reply index

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-20 15:12 [RFT][PATCH v7 0/8] sched/cpuidle: Idle loop rework Rafael J. Wysocki
2018-03-20 15:13 ` [RFT][PATCH v7 1/8] time: tick-sched: Reorganize idle tick management code Rafael J. Wysocki
2018-03-20 15:15 ` [RFT][PATCH v7 2/8] sched: idle: Do not stop the tick upfront in the idle loop Rafael J. Wysocki
2018-03-20 15:15 ` [RFT][PATCH v7 3/8] " Rafael J. Wysocki
2018-03-20 18:00   ` [Correction][RFT][PATCH v7 3/8] sched: idle: Do not stop the tick before cpuidle_idle_call() Rafael J. Wysocki
2018-03-20 15:16 ` [RFT][PATCH v7 4/8] jiffies: Introduce USER_TICK_USEC and redefine TICK_USEC Rafael J. Wysocki
2018-03-20 15:45 ` [RFT][PATCH v7 5/8] cpuidle: Return nohz hint from cpuidle_select() Rafael J. Wysocki
2018-03-21  6:48   ` [RFT][PATCH v7.1 " Rafael J. Wysocki
2018-03-21 11:52     ` Rafael J. Wysocki
2018-03-21 13:03   ` [RFT][PATCH v7.2 " Rafael J. Wysocki
2018-03-21 14:36   ` [RFT][PATCH v7 " Rafael J. Wysocki
2018-03-21 17:59     ` Thomas Ilsche
2018-03-21 22:15       ` Rafael J. Wysocki
2018-03-22 13:18         ` Thomas Ilsche
2018-03-22 17:23           ` Rafael J. Wysocki
2018-03-22  6:24       ` Doug Smythies
2018-03-22 15:41       ` Doug Smythies
2018-03-22 17:21         ` Rafael J. Wysocki
2018-03-21 18:23     ` Doug Smythies
2018-03-22 17:40   ` [RFT][PATCH v7.3 " Rafael J. Wysocki
2018-03-28  9:14     ` Thomas Ilsche
2018-03-30  9:39       ` Rafael J. Wysocki
2018-04-10 15:22         ` Thomas Ilsche
2018-03-22 20:46   ` Doug Smythies
2018-03-20 15:45 ` [RFT][PATCH v7 6/8] sched: idle: Select idle state before stopping the tick Rafael J. Wysocki
2018-03-27 21:50   ` Thomas Ilsche
2018-03-27 22:10     ` Rafael J. Wysocki
2018-03-28  8:13       ` Rafael J. Wysocki
2018-03-28  8:38         ` Thomas Ilsche
2018-03-28 10:37           ` Rafael J. Wysocki
2018-03-28 10:56             ` Rafael J. Wysocki
2018-03-28 15:15               ` Thomas Ilsche
2018-03-28 20:41               ` Doug Smythies
2018-03-28 23:11                 ` Rafael J. Wysocki [this message]
2018-03-20 15:46 ` [RFT][PATCH v7 7/8] cpuidle: menu: Refine idle state selection for running tick Rafael J. Wysocki
2018-03-20 15:47 ` [RFT][PATCH v7 8/8] cpuidle: menu: Avoid selecting shallow states with stopped tick Rafael J. Wysocki
2018-03-20 17:52 ` [RFT][PATCH v7 3/8] sched: idle: Do not stop the tick upfront in the idle loop Doug Smythies
2018-03-20 18:01   ` Rafael J. Wysocki
2018-03-21 12:31 ` [RFT][PATCH v7 0/8] sched/cpuidle: Idle loop rework Rik van Riel
2018-03-21 13:55   ` Rafael J. Wysocki
2018-03-21 14:53     ` Rik van Riel

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