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Date: Sat, 14 Apr 2007 15:27:32 +0200
From: Willy Tarreau <w@1wt.eu>
To: Ingo Molnar <mingo@elte.hu>
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>
Subject: Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]
Message-ID: <20070414132732.GA22103@1wt.eu>
References: <20070413202100.GA9957@elte.hu> <20070414020424.GB14544@wotan.suse.de> <20070414063254.GB14875@elte.hu> <20070414064334.GA19463@elte.hu> <20070414080833.GL943@1wt.eu> <20070414083625.GM943@1wt.eu> <20070414105338.GB19454@elte.hu> <20070414130101.GA2538@1wt.eu>
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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 :-/

I'll investigate a bit.

Willy