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

[Con Kolivas <kernel@kolivas.org>]

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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