linux-kernel - Re: + kmod-remove-unecessary-explicit-wide-cpu-affinity-setting.patch added to -mm tree

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Message-ID: <20150708125209.GA9181@lerouge>
Date:	Wed, 8 Jul 2015 14:52:10 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	akpm@...ux-foundation.org, cl@...ux.com, riel@...hat.com,
	rusty@...tcorp.com.au, tj@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: +
 kmod-remove-unecessary-explicit-wide-cpu-affinity-setting.patch added to -mm
 tree

On Wed, Jul 08, 2015 at 01:32:26AM +0200, Oleg Nesterov wrote:
> Well, sorry for noise.
> 
> Let me repeat that I agree with this change, but...
> 
> On 07/07, Andrew Morton wrote:
> >
> > From: Frederic Weisbecker <fweisbec@...il.com>
> > Subject: kmod: remove unecessary explicit wide CPU affinity setting
> >
> > Not only useless it even breaks nohz full.  The housekeeping work (general
> > kernel internal code that user doesn't care much about) is handled by a
> > reduced set of CPUs in nohz full, precisely those that are not included by
> > nohz_full= kernel parameters.  For example unbound workqueues are handled
> > by housekeeping CPUs.
> 
> I still think this part of the changelog looks confusing and just wrong.

I agree!

> 
> It is not that it breaks nohz full, unbound workqueues have nothing to
> do with housekeeping_mask from the kernel pov. But yes, people can change
> ->cpumask and this can connect to housekeeping_mask.

Right. In fact that's the motivation of the patch but the connection is
much more indirect than what the changelog suggests. So I'll fix the changelog.

> 
> Frederic, may I ask you to update the changelog? Although perhaps it was
> just me who was confused...

Sure! I think Andrew applied the patches to keep track of them and make sure
they don't get lost. But I'm working on a new iteration to replace them.

Thanks!

> Oleg.
> 
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