Message-ID: <1502433388.16425.9.camel@gmx.de>
Subject: Re: [RFC PATCH 0/9] Introduce housekeeping subsystem
From: Mike Galbraith <efault@gmx.de>
To: Chris Metcalf <cmetcalf@mellanox.com>,
        Frederic Weisbecker <fweisbec@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Luiz Capitulino <lcapitulino@redhat.com>,
        Christoph Lameter <cl@linux.com>,
        "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
        Ingo Molnar <mingo@kernel.org>, Rik van Riel <riel@redhat.com>,
        Wanpeng Li <kernellwp@gmail.com>
Date: Fri, 11 Aug 2017 08:36:28 +0200
In-Reply-To: <3398d7d6-74c2-4918-ae3d-aa5a2e3a12dd@mellanox.com>
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         <f50f9cb3-a3ea-3e2e-9b0a-ebb9af900568@mellanox.com>
         <20170810125437.GA8754@lerouge>
         <3398d7d6-74c2-4918-ae3d-aa5a2e3a12dd@mellanox.com>
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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.

Personally, I think NOHZ_FULL_ALL should just die.

	-Mike