linux-kernel - Re: [PATCH] kthread: Don't depend on work queues

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Message-ID: <m1lkgysrdb.fsf@ebiederm.dsl.xmission.com>
Date:	Wed, 11 Apr 2007 12:22:40 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Oleg Nesterov <oleg@...sign.ru>,
	Davide Libenzi <davidel@...ilserver.org>,
	Jan Engelhardt <jengelh@...ux01.gwdg.de>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Robin Holt <holt@....com>, Roland McGrath <roland@...hat.com>,
	"Serge E. Hallyn" <serge@...lyn.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kthread: Don't depend on work queues

Andrew Morton <akpm@...ux-foundation.org> writes:

> argh.  Your description freely confuddles the terms "kernel thread" and
> "kthread".  Can we not do that?  Henceforth the term "kernel thread" refers
> to something which was started with kernel_thread() and "kthread" refers to
> something which was created by kthread_create(), OK?

Yes.  Will fix.

> Your patch gets midly tangled up with Oleg's recent
>
> reduce-reparent_to_init.patch
> make-kernel-threads-invisible-to-sbin-init.patch
> reparent-kernel-threads-to-swapper.patch
>
> but they seemed fairly unpopular anyway so I'll drop 'em.

Ok.  I kind of liked the first one but that is a minor cleanup.

> Your wait_event() will contribute to load average, I expect.  We get mail. 
> I converted it to wait_event_interruptible().

Ok.  That is more polite.

> I guess using PF_NOFREEZE rather than try_to_freeze() is OK, but one
> wonders what thinking led to that?

That is what we are currently doing for the work queues, and I was lazy.
For people who care they can fix it.

> Often when we have a singleton thread like this it is neater to use
> wake_up_process() directly on it, rather than creating a rather pointless
> waitqueue_head for it.  I started looking into that but it would have taken
> more than 30 seconds.

Sure I took a look and it isn't too hard.  Updated patch in a minute...

I have left the locking the way it is despite the reasonable chance that
Oleg points I can only acquire the lock when deleting the list entry.
I'm to lazy to think through the SMP races to make certain that is safe.

Eric




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