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

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Date:	Sat, 14 Apr 2007 20:18:54 +0200
From:	Willy Tarreau <w@....eu>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	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>,
	Jiri Slaby <jirislaby@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]

On Sat, Apr 14, 2007 at 07:54:33PM +0200, Ingo Molnar wrote:
> 
> * Eric W. Biederman <ebiederm@...ssion.com> wrote:
> 
> > > Thinking about it, I don't know if there are calls to schedule() 
> > > while switching from tty1 to tty2. Alt-F2 had no effect anymore, and 
> > > "chvt 2" simply blocked. It would have been possible that a 
> > > schedule() call somewhere got starved due to the load, I don't know.
> > 
> > It looks like there is a call to schedule_work.
> 
> so this goes over keventd, right?
> 
> > There are two pieces of the path. If you are switching in and out of a 
> > tty controlled by something like X.  User space has to grant 
> > permission before the operation happens.  Where there isn't a gate 
> > keeper I know it is cheaper but I don't know by how much, I suspect 
> > there is still a schedule happening in there.
> 
> Could keventd perhaps be starved? Willy, to exclude this possibility, 
> could you perhaps chrt keventd to RT priority? If events/0 is PID 5 then 
> the command to set it to SCHED_FIFO:50 would be:
> 
>   chrt -f -p 50 5
> 
> but ... events/0 is reniced to -5 by default, so it should definitely 
> not be starved.

Well, since I merged the fair-fork patch, I cannot reproduce (in fact,
bash forks 1000 processes, then progressively execs scheddos, but it
takes some time). So I'm rebuilding right now. But I think that Linus
has an interesting clue about GPM and notification before switching
the terminal. I think it was enabled in console mode. I don't know
how that translates to frozen xterms, but let's attack the problems
one at a time.

Willy

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