linux-kernel - Re: [PATCH 1/4] kthreads: move sched-realeted initialization from kthreadd context

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Message-ID: <20090201103817.GB5728@redhat.com>
Date:	Sun, 1 Feb 2009 11:38:17 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@....de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...e.hu>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Vitaliy Gusev <vgusev@...nvz.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] kthreads: move sched-realeted initialization from
	kthreadd context

On 01/31, Rusty Russell wrote:
>
> On Friday 30 January 2009 23:03:50 Oleg Nesterov wrote:
> > (on top of kthread-dont-looking-for-a-task-in-create_kthread-2.patch)
>
> Hi Oleg,
>
>    Thanks for the cc: Vitaliy, I never saw that patch.  I've included it in my queue now.
>
> As to this patch, it seems marginal.  I've never been convinced that we should
> be trying to rescue root if they choose to set kthreadd's prio anyway,

I agree. Personally, I never understood this too. But if we want to
remove this code we need the separate discussion, so I just moved it
to the caller's context.

> but I'm also wondering why we care about kthread_create scalability!

It is always better to speedup things and to decrease the latency ;)

But I also think this and the next patch make the code simpler and
more clean. Now the only thing create_kthread() does is a plain fork()
and nothing else, this is imho good.

> Still, I'm happy to apply it with one change:
>
> > +		/*
> > +		 * root may have changed our (kthreadd's) priority or CPU mask.
> > +		 * The kernel thread should not inherit these properties.
> > +		 */
> > +		sched_setscheduler_nocheck(create.result, SCHED_NORMAL, &param);
> > +		set_user_nice(create.result, KTHREAD_NICE_LEVEL);
> > +		set_cpus_allowed_ptr(create.result, CPU_MASK_ALL_PTR);
>
> cpu_all_mask is the non-deprecated replacement for CPU_MASK_ALL_PTR.

Great, thanks.

(btw, I thought about avoiding CPU_MASK_ALL_PTR too, but I didn't
 dare to mix 2 different things in one patch).

Oleg.

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