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

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Message-ID: <20070414175433.GA17527@elte.hu>
Date:	Sat, 14 Apr 2007 19:54:33 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Willy Tarreau <w@....eu>, 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]


* 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.

	Ingo
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