keventd gives exceptional priority to usermode helpers

keventd gives exceptional priority to usermode helpers

[Jan Engelhardt]

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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@linux01.gwdg.de>



Jan Engelhardt
-- 
ENOSPC

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#==============================================================================
# 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)

Re: keventd gives exceptional priority to usermode helpers

[Chris Wright]

* Jan Engelhardt (jengelh@linux01.gwdg.de) wrote:
> --- 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);

Seems reasonable.  Although, I don't see a niceval of -20, but -5 on
keventd (workqueues do set_user_nice(-5)).  Also, this patch is
whitespace damaged, should be tab not spaces.

thanks,
-chris
-- 
Linux Security Modules     http://lsm.immunix.org     http://lsm.bkbits.net

Re: keventd gives exceptional priority to usermode helpers

[Jan Engelhardt]

>> @@ -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);
>
>Seems reasonable.  Although, I don't see a niceval of -20, but -5 on
>keventd (workqueues do set_user_nice(-5)).  Also, this patch is

Right, `ps` only shows "<" for <0, "" for 0 and "N" for >0. But -5 is still a 
hard thing.

>whitespace damaged, should be tab not spaces.

the neverending debate...



Jan Engelhardt
-- 
ENOSPC

Re: keventd gives exceptional priority to usermode helpers

[Jan Engelhardt]

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Signed-off-by: Jan Engelhardt <jengelh@linux01.gwdg.de>


--- linux-2.6.8-20041204030200/kernel/kmod.c	2004-12-06 14:28:44.000000000 +0100
+++ 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)




Jan Engelhardt
-- 
ENOSPC

[-- Attachment #2: Type: TEXT/PLAIN, Size: 1198 bytes --]

#==============================================================================
# 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
#==============================================================================
#
# - udev and friends need a fair amount of CPU, and really bring down the
#   system when they run -- usually in nice -5
#   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
--- linux-2.6.8-20041204030200/kernel/kmod.c	2004-12-06 14:28:44.000000000 +0100
+++ 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)