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

Con Kolivas
2007-04-21T15:56:47Z

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