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Date: Sat, 14 Apr 2007 18:19:27 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Willy Tarreau <w@1wt.eu>
Cc: Nick Piggin <npiggin@suse.de>, linux-kernel@vger.kernel.org,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Con Kolivas <kernel@kolivas.org>, Mike Galbraith <efault@gmx.de>,
       Arjan van de Ven <arjan@infradead.org>,
       Thomas Gleixner <tglx@linutronix.de>,
       "Eric W. Biederman" <ebiederm@xmission.com>,
       Jiri Slaby <jirislaby@gmail.com>, Alan Cox <alan@lxorguk.ukuu.org.uk>
Subject: Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]
Message-ID: <20070414161927.GD3099@elte.hu>
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* Willy Tarreau <w@1wt.eu> wrote:

> On Sat, Apr 14, 2007 at 03:01:01PM +0200, Willy Tarreau wrote:
> > 
> > Well, I'll stop heating the room for now as I get out of ideas about how
> > to defeat it.
> 
> Ah, I found something nasty.
> If I start large batches of processes like this :
> 
> $ for i in $(seq 1 1000); do ./scheddos2 4000 4000 & done
> 
> the ramp up slows down after 700-800 processes, but something very 
> strange happens. If I'm under X, I can switch the focus to all xterms 
> (the WM is still alive) but all xterms are frozen. On the console, 
> after one moment I simply cannot switch to another VT anymore while I 
> can still start commands locally. But "chvt 2" simply blocks. SysRq-K 
> killed everything and restored full control. Dmesg shows lots of :

> SAK: killed process xxxx (scheddos2): process_session(p)==tty->session.
> 
> I wonder if part of the problem would be too many processes bound to 
> the same tty :-/

hm, that's really weird. I've Cc:-ed the tty experts (Erik, Jiri, Alan), 
maybe this description rings a bell with them?

	Ingo