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

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Message-ID: <20160912161444.GA5008@twins.programming.kicks-ass.net>
Date:   Mon, 12 Sep 2016 18:14:44 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Chris Metcalf <cmetcalf@...lanox.com>
Cc:     Francis Giraldeau <francis.giraldeau@...il.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,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: Ping: [PATCH v15 00/13] support "task_isolation" mode

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. Is there
> >a way to suppress this irq_work? Should we run the isolated task with
> >high real-time priority, such that it never get preempted?
> 
> On the tile platform we don't have the frequency scaling stuff to contend with, so
> I don't know much about it.  I'd be very curious to know what you can figure out
> on this front.

Rafael, I'm thinking the performance governor should be able to run
without sending IPIs. Is there anything we can quickly do about that?