linux-kernel - Re: Ping: [PATCH v15 00/13] support "task

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Date:   Tue, 13 Sep 2016 12:00:33 -0400
From:   Francis Giraldeau <francis.giraldeau@...il.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Chris Metcalf <cmetcalf@...lanox.com>,
        Gilad Ben Yossef <giladb@...lanox.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Rik van Riel <riel@...hat.com>, Tejun Heo <tj@...nel.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Christoph Lameter <cl@...ux.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...capital.net>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-doc@...r.kernel.org, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Ping: [PATCH v15 00/13] support "task_isolation" mode

On 2016-09-12 08:05 PM, Rafael J. Wysocki wrote:
> On Monday, September 12, 2016 11:15:45 PM Rafael J. Wysocki wrote:
>> On Monday, September 12, 2016 06:14:44 PM Peter Zijlstra wrote:
>>> On Mon, Sep 12, 2016 at 12:01:58PM -0400, Chris Metcalf wrote:
>>>> On 9/7/2016 5:11 PM, Francis Giraldeau wrote:
>>>>> When running only the test_jitter(), the isolation mode is lost:
>>>>>
>>>>>     [ 6741.566048] isolation/9515: task_isolation mode lost due to irq_work
>>>>>
>>>>> With ftrace (events/workqueue/workqueue_execute_start), I get a bit more info:
>>>>>
>>>>>      kworker/1:1-676   [001] ....  6610.097128: workqueue_execute_start: work struct ffff8801a784ca20: function dbs_work_handler
>>>>>
>>>>> The governor was ondemand, so I tried to set the frequency scaling
>>>>> governor to performance, but that does not solve the issue.
>>>
>>> Rafael, I'm thinking the performance governor should be able to run
>>> without sending IPIs. Is there anything we can quickly do about that?
>>
>> The performance governor doesn't do any IPIs.
>>
>> At this point I'm not sure what's going on.
> 
> I've just tried and switching over to the performance governor makes
> dbs_work_handler go away for me (w/ -rc4 with some extra irrelevant patches
> on top) as it should.

Ho gosh, the command "cpufreq-set -g performance" sets the governor only
for cpu0. I was expecting it to set for all cpus. The isolation test runs
on cpu1 and this cpu was still with ondemand governor. With performance
governor, the dbs_work_handler does not occurs anymore and the isolated
task is not preempted by that kworker thread anymore.

Sorry for the noise and thanks for checking!

Francis