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

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Message-ID: <20160927144943.GE6242@lerouge>
Date:   Tue, 27 Sep 2016 16:49:45 +0200
From:   Frederic Weisbecker <fweisbec@...il.com>
To:     Francis Giraldeau <francis.giraldeau@...il.com>
Cc:     Chris Metcalf <cmetcalf@...lanox.com>,
        Gilad Ben Yossef <giladb@...lanox.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Rik van Riel <riel@...hat.com>, Tejun Heo <tj@...nel.org>,
        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 Mon, Sep 12, 2016 at 08:20:16PM -0400, Francis Giraldeau wrote:
> 
> The args are valid, but the system has an unstable clock, therefore the
> operation is not supported. In the user point of view, maybe ENOTSUPP
> would be more appropriate? But then, we need to check the reason and
> can_stop_my_full_tick() returns only a boolean.
> 
> On a side note, the NOSIG mode may be confusing for the users. At first,
> I was expecting that NOSIG behaves the same way as the normal task isolation
> mode. In the current situation, if the user wants the normal behavior, but
> does not care about the signal, the user must register an empty signal handler.
> 
> However, if I understand correctly, other settings beside NOHZ and isolcpus
> are required to support quiet CPUs, such as irq_affinity and rcu_nocb. It would
> be very convenient from the user point of view if these other settings were configure
> correctly.
> 
> I can work on that and also write some doc (Documentation/task-isolation.txt ?).

That would be lovely! Part of this documentation already exists in
Documentation/timers/NO_HZ.txt and also in Documentation/kernel-per-CPU-kthreads.txt

I think we should extract the isolation informations that aren't related to the tick
from NO_HZ.txt and put them in task-isolation.txt, perhaps merge kernel-per-CPU-kthreads.txt
into it or at least add a pointer to it. Then add all the missing informations as many things
have evolved since then.

I'll gladly help.

Thanks.