linux-kernel - Re: [RFC PATCH 0/9] Introduce housekeeping subsystem

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Message-ID: <3398d7d6-74c2-4918-ae3d-aa5a2e3a12dd@mellanox.com>
Date:   Thu, 10 Aug 2017 09:57:37 -0400
From:   Chris Metcalf <cmetcalf@...lanox.com>
To:     Frederic Weisbecker <fweisbec@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Luiz Capitulino <lcapitulino@...hat.com>,
        Christoph Lameter <cl@...ux.com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>, Mike Galbraith <efault@....de>,
        Rik van Riel <riel@...hat.com>,
        Wanpeng Li <kernellwp@...il.com>
Subject: Re: [RFC PATCH 0/9] Introduce housekeeping subsystem

On 8/10/2017 8:54 AM, Frederic Weisbecker wrote:
> But perhaps I should add a new NO_HZ_FULL_BUT_HOUSEKEEPING option.
> Otherwise we'll change the meaning of NO_HZ_FULL_ALL way too much, to the point
> that its default behaviour will be the exact opposite of the current one: by default
> every CPU is housekeeping, so NO_HZ_FULL_ALL would have no effect anymore if we
> don't set housekeeping boot option.

Maybe a CONFIG_HOUSEKEEPING_BOOT_ONLY as a way to restrict housekeeping
by default to just the boot cpu.  In conjunction with NOHZ_FULL_ALL you would
then get the expected semantics.

> Also I plan to add a housekeeping option to offload the residual 1Hz tick from
> nohz_full CPUs. So having "housekeeping=0,tick_offload" would make CPU 0 the
> housekeeper, make the other CPUs nohz_full and handle their 1hz tick from CPU 0.

It does seem like that might be implied by requesting NOHZ_FULL on the core...
or maybe it's just implied by TASK_ISOLATION.  I've done a bad job of finding time
to work on that since last year's Plumbers, but September looks good :)

-- 
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com