linux-kernel - Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]

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Date:	Sat, 14 Apr 2007 15:27:32 +0200
From:	Willy Tarreau <w@....eu>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Nick Piggin <npiggin@...e.de>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Con Kolivas <kernel@...ivas.org>,
	Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]

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

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