linux-kernel - Re: [PATCH 2/5] kmod: Use system_unbound

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Message-ID: <20150709224406.GA17528@redhat.com>
Date:	Fri, 10 Jul 2015 00:44:06 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux.com>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/5] kmod: Use system_unbound_wq instead of khelper

On 07/09, Frederic Weisbecker wrote:
>
> We need to launch the usermodehelper kernel threads with the widest
> affinity and this is why we have khelper for. This workqueue has unbound
> properties and thus a wide affinity inherited by all its children.
>
> Now khelper also has special properties that we aren't much interested
> in: ordered and singlethread. There is really no need about ordering as
> all we do is creating kernel threads. This can be done concurrently.
> And singlethread is a useless limitation as well.
>
> The workqueue engine already proposes generic unbound workqueues that
> don't share these useless properties and handle well parallel jobs.
>
> Lets just use them.
>
> Suggested-by: Oleg Nesterov <oleg@...hat.com>

Well yes, but it seems that you missed another part of my email ;)

If we just change usermodehelper to use system_unbound_wq then we
probably should keep set_cpus_allowed_ptr() removed by 4/5.

Note that system_unbound_wq has ->no_numa == F, so its worker threads
are NUMA bound. Perhaps this is not that bad, I do not know. But at
least this means that 4/5 needs more documentation/justification.

But as for this particular patch I obviously like it, khelper_wq
must die imo ;)

Oleg.

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