linux-kernel - Re: [REPORT] cfs-v4 vs sd-0.44

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Date:	Sun, 22 Apr 2007 01:55:20 +1000
From:	Con Kolivas <kernel@...ivas.org>
To:	Willy Tarreau <w@....eu>,
	William Lee Irwin III <wli@...omorphy.com>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>, Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Williams <pwil3058@...pond.net.au>,
	Thomas Gleixner <tglx@...utronix.de>, caglar@...dus.org.tr,
	Gene Heskett <gene.heskett@...il.com>
Subject: Re: [REPORT] cfs-v4 vs sd-0.44

On Saturday 21 April 2007 22:12, Willy Tarreau wrote:
> I promised to perform some tests on your code. I'm short in time right now,
> but I observed behaviours that should be commented on.

>   Feels even better, mouse movements are very smooth even under high load.
>   I noticed that X gets reniced to -19 with this scheduler. I've not looked
>   at the code yet but this looked suspicious to me.

Looks like this code does it:

+int sysctl_sched_privileged_nice_level __read_mostly = -19;

allows anything that sets sched_privileged_task one way or another gets 
nice -19, and this is enabled by default.

--- linux-cfs-2.6.20.7.q.orig/arch/i386/kernel/ioport.c
+++ linux-cfs-2.6.20.7.q/arch/i386/kernel/ioport.c

+	if (turn_on) {
+		if (!capable(CAP_SYS_RAWIO))
+			return -EPERM;
+		/*
+		 * Task will be accessing hardware IO ports,
+		 * mark it as special with the scheduler too:
+		 */
+		sched_privileged_task(current);
+	}

presumably that selects out X as a privileged task... and sets it to nice -19 
by default.

-- 
-ck
-
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