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

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Message-ID: <20170811150129.GB25912@lerouge>
Date:   Fri, 11 Aug 2017 17:01:30 +0200
From:   Frederic Weisbecker <fweisbec@...il.com>
To:     Mike Galbraith <efault@....de>
Cc:     Chris Metcalf <cmetcalf@...lanox.com>,
        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 Fri, Aug 11, 2017 at 08:36:28AM +0200, 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.

Indeed we probably shouldn't introduce new config that affine housekeeping to a
single CPU.

> Personally, I think NOHZ_FULL_ALL should just die.

Yeah, although it's still useful for automatic boot testing to detect issues
with nohz_full on.

Thanks.