linux-kernel - Re: [PATCH 0/5] kmod: Cleanups, simplifications, and make isolation friendly v3

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Message-ID: <20150727184840.GB16393@mtj.duckdns.org>
Date:	Mon, 27 Jul 2015 14:48:40 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Christoph Lameter <cl@...ux.com>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 0/5] kmod: Cleanups, simplifications, and make isolation
 friendly v3

On Mon, Jul 27, 2015 at 06:27:15PM +0200, Frederic Weisbecker wrote:
> Hence those two debatable changes:
> 
> _ We would like to use generic workqueues. System unbound workqueues are
>   a very good candidate but they are not wide affine, only node affine.
>   Now probably a node is enough to perform many parallel kmod jobs.

If being node-affine is an issue, kmod can easily create a workqueue
w/o NUMA affinity using apply_workqueue_attrs() with no_numa set to
%true.

> _ We would like to remove the wait_for_helper kernel thread (UMH_WAIT_PROC
>   handler) to use the workqueue. It means that if the workqueue blocks,
>   and no other worker can take pending kmod request, we can be screwed.
>   Now if we have 512 threads, this should be enough.

The maximum number of worker can also be raised on the workqueue.
That said, I don't think we want to.

IMHO, system_wq should be fine and if it isn't turning off numa
affinity or raising max worker limit later is pretty trivial.

Thanks.

-- 
tejun
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