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

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Date:   Fri, 11 Aug 2017 11:08:09 -0400
From:   Chris Metcalf <cmetcalf@...lanox.com>
To:     Mike Galbraith <efault@....de>,
        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>, Rik van Riel <riel@...hat.com>,
        Wanpeng Li <kernellwp@...il.com>
Subject: Re: [RFC PATCH 0/9] Introduce housekeeping subsystem

On 8/11/2017 2:36 AM, Mike Galbraith wrote:
> On Thu, 2017-08-10 at 09:57 -0400, Chris Metcalf wrote:
>> 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.
> A big box with only the boot cpu for housekeeping is likely screwed.

Fair point - this kind of configuration would be primarily useful for
dedicated systems that were running a high-traffic-rate networking
application on many cores, for example.  In this mode you don't end up
putting a lot of burden on the housekeeping core.  In any case,
probably not worth adding an additional kernel config for.

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