linux-kernel - Re: [RFT][PATCH v7 6/8] sched: idle: Select idle state before stopping the tick

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Date:   Wed, 28 Mar 2018 17:15:11 +0200
From:   Thomas Ilsche <thomas.ilsche@...dresden.de>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
CC:     Peter Zijlstra <peterz@...radead.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Doug Smythies <dsmythies@...us.net>,
        Rik van Riel <riel@...riel.com>,
        "Aubrey Li" <aubrey.li@...ux.intel.com>,
        Mike Galbraith <mgalbraith@...e.de>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFT][PATCH v7 6/8] sched: idle: Select idle state before
 stopping the tick

On 2018-03-28 12:56, Rafael J. Wysocki wrote:
> On Wed, Mar 28, 2018 at 12:37 PM, Rafael J. Wysocki <rafael@...nel.org> wrote:
>> On Wed, Mar 28, 2018 at 10:38 AM, Thomas Ilsche
>> <thomas.ilsche@...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.


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