linux-kernel - Re: [PATCH] kthread: Don't looking for a task in create

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Message-ID: <20090121153355.GA19169@redhat.com>
Date:	Wed, 21 Jan 2009 16:33:55 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Vitaliy Gusev <vgusev@...nvz.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org,
	Pavel Emelyanov <xemul@...nvz.org>
Subject: Re: [PATCH] kthread: Don't looking for a task in create_kthread()
	#2

On 01/20, Vitaliy Gusev wrote:
>
> Ok, I understand you. You want to decrease kthreadd latency. In this case
> your suggestion is right.

Please feel free to send the patch then.

> > OK, please forget. This reminds me kthread.c needs a major rework
> > anyway, hopefully I'll try to do this soon.
>
> I also have intent to make kthread_run/kthread_create more easy used for
> threads that exit himself on error.
> For example, we create some thread THR, which does something but exits on error.
> So in normal case we need to call kthread_stop() to stop thread THR, but on
> error we don't. This is a problem, because we can't simple (without race) 
> determine that THR was exited.

This is only one of the problems,

> Simple workaround - do a sleeping loop in thread THR and don't exit until kthread_should_stop.
> But it isn't a good for code reading/writing.
>
> So my suggestion is: Move workaround sleeping logic from THR to low level
> functions:
>    wait for a kthread_should_stop in kthread() if THR was exited.

I think it is better to improve kthread_stop() so it can be used even
if kthread has already exited, this is not that hard.

But there are other problems, I'll try to provide mor info later.

Oleg.

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