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

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

[Oleg Nesterov]

Well, sorry for noise.

Let me repeat that I agree with this change, but...

On 07/07, Andrew Morton wrote:
>
> From: Frederic Weisbecker <fweisbec@gmail.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.

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.

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

Oleg.

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

[Frederic Weisbecker]

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@gmail.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.
>