linux-kernel - Re: init's children list is long and slows reaping children.

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Date:	Tue, 10 Apr 2007 04:42:04 -0500
From:	Robin Holt <holt@....com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jeff Garzik <jeff@...zik.org>, Robin Holt <holt@....com>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Jack Steiner <steiner@...ricas.sgi.com>
Subject: Re: init's children list is long and slows reaping children.

On Mon, Apr 09, 2007 at 06:48:54PM -0600, Eric W. Biederman wrote:
> Andrew Morton <akpm@...ux-foundation.org> writes:
> 
> > I suspect there are quite a few kernel threads which don't really need to
> > be threads at all: the code would quite happily work if it was changed to
> > use keventd, via schedule_work() and friends.  But kernel threads are
> > somewhat easier to code for.
> >
> > I also suspect that there are a number of workqueue threads which
> > could/should have used create_singlethread_workqueue().  Often this is
> > because the developer just didn't think to do it.
> >
> > otoh, a lot of these inefficeincies are probably down in scruffy drivers
> > rather than in core or top-level code.
> >
> > <I also wonder where all these parented-by-init,
> > presumably-not-using-kthread kernel threads are coming from>
> 
> 
> >From another piece of this thread.
> 
> > > Robin how many kernel thread per cpu are you seeing?
> > 
> > 10.
> > 
> > FYI, pid 1539 is kthread.
> > 
> > a01:~ # ps -ef | egrep "\[.*\/255\]" 
> > root       512     1  0 Apr08 ?        00:00:00 [migration/255]
> > root       513     1  0 Apr08 ?        00:00:00 [ksoftirqd/255]
> > root      1281     1  0 Apr08 ?        00:00:02 [events/255]
> > root      2435  1539  0 Apr08 ?        00:00:00 [kblockd/255]
> > root      3159  1539  0 Apr08 ?        00:00:00 [aio/255]
> > root      4007  1539  0 Apr08 ?        00:00:00 [cqueue/255]
> > root      8653  1539  0 Apr08 ?        00:00:00 [ata/255]
> > root     17438  1539  0 Apr08 ?        00:00:00 [xfslogd/255]
> > root     17950  1539  0 Apr08 ?        00:00:00 [xfsdatad/255]
> > root     18426  1539  0 Apr08 ?        00:00:00 [rpciod/255]
> 
> 
> So it looks like there were about 1500 kernel threads that started up before
> kthread started.

I should have been more clear, this is from that 4096 broken down to a
512 cpu partition.  This is the configuration the customer will receive
the machine.  The 4096 was just to see if it worked.

> So the kernel threads appear to have init as their parent is because
> they started before kthread for the most part.
> 
> At 10 kernel threads per cpu there may be a little bloat but it isn't
> out of control.  It is mostly that we are observing the kernel as
> NR_CPUS approaches infinity.  4096 isn't infinity yet but it's easily
> a 1000 fold bigger then most people are used to :)
> 
> Eric
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