keventd gives exceptional priority to usermode helpers

[Jan Engelhardt]

Hi,


on SUSE 9.2, we experienced that plugging in an USB stick slows the system 
down considerably. In the end, I tracked (one half of the problem) down to 
kernelspace, where keventd starts the /sbin/hotplug usermode helper with 
priority -20. This is bad because hotplug, udev or the programs that ship with 
the whole hotplug subsystem (possibly including SUSE's own scripts) require 
some CPU -- and with nice -20 get it definitely.

keventd itself should stay at nice level -20, since it also spawns kreiserfsd, 
just to name one. So the (attached) patch reprioritizes *user*mode 
helpers/tasks back to nice 0.

Signed-off-by: Jan Engelhardt <jengelh@xxxxxxxxxxxxxxx>



Jan Engelhardt
-- 
ENOSPC#==============================================================================
# Linux 2.6-HX MODIFICATION
#   Copyright (C) Jan Engelhardt <jengelh [at] linux01 gwdg de>, 2004
#   -- License restrictions apply (GPL2)
#   -- For details see doc/GPL2.txt.
#   http://linux01.org:2222/prog-hxtools.php
#==============================================================================
# File:  utf8fix.diff
# Class:
#
# - udev and friends need a fair amount of CPU, and really bring down the
#   system when they run -- usually in nice -20
#   Fix it in that usermode helpers always get nice 0 by default
#
#------------------------------------------------------------------------------
diff -dpu usr_A/src/kotd/linux-2.6.8-20041204030200/kernel/kmod.c usr_B/src/kotd/linux-2.6.8-20041204030200/kernel/kmod.c
--- usr_A/src/kotd/linux-2.6.8-20041204030200/kernel/kmod.c	2004-12-06 14:28:44.000000000 +0100
+++ usr_B/src/kotd/linux-2.6.8-20041204030200/kernel/kmod.c	2005-01-06 11:44:04.130600000 +0100
@@ -165,6 +165,7 @@ static int ____call_usermodehelper(void 
 
 	/* We can run anywhere, unlike our parent keventd(). */
 	set_cpus_allowed(current, CPU_MASK_ALL);
+        set_user_nice(current, 0);
 
 	retval = -EPERM;
 	if (current->fs->root)