Bug 146789

Version:            (using KDE KDE 3.5.6)
Installed from:    Debian testing/unstable Packages

Reported in Debian BTS at http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=364119
(not sure if assigned to the right application.)

I got a report from a laptop-mode-tools user saying that kwin kept his 
disk spun up. I checked his logs, and indeed it seems to be the case 
that his kwin process explicitly syncs pretty regularly. I straced my 
own kwin to confirm this behaviour, and I see the following:

open("/home/bsamwel/.kde/share/config/kwinrulesrc6EREMa.new", 
O_RDWR|O_CREAT|O_EXCL, 0600) = 11
umask(0)                                = 022
umask(022)                              = 0
fchmod(11, 0600)                        = 0
getgid32()                              = 1000
getuid32()                              = 1000
fchown32(11, 1000, 1000)                = 0
fcntl64(11, F_SETFD, FD_CLOEXEC)        = 0
stat64("/home/bsamwel/.kde/share/config/kwinrulesrc", 
{st_mode=S_IFREG|0600, st_size=824, ...}) = 0
getuid32()                              = 1000
getgid32()                              = 1000
fchmod(11, 0100600)                     = 0
fchmod(11, 0600)                        = 0
fcntl64(11, F_GETFL)                    = 0x2 (flags O_RDWR)
fstat64(11, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 
0) = 0xb6705000
_llseek(11, 0, [0], SEEK_CUR)           = 0
write(11, "[1]\ndescription=(Default) Disabl"..., 824) = 824
fdatasync(11)                           = 0
close(11)                               = 0
munmap(0xb6705000, 4096)                = 0
rename("/home/bsamwel/.kde/share/config/kwinrulesrc6EREMa.new", 
"/home/bsamwel/.kde/share/config/kwinrulesrc") = 0


and then:


open("/home/bsamwel/.kde/share/config/kdeglobalsZbum9a.new", 
O_RDWR|O_CREAT|O_EXCL, 0600) = 11
umask(0)                                = 022
umask(022)                              = 0
fchmod(11, 0600)                        = 0
getgid32()                              = 1000
getuid32()                              = 1000
fchown32(11, 1000, 1000)                = 0
fcntl64(11, F_SETFD, FD_CLOEXEC)        = 0
stat64("/home/bsamwel/.kde/share/config/kdeglobals", 
{st_mode=S_IFREG|0600, st_size=5804, ...}) = 0
getuid32()                              = 1000
getgid32()                              = 1000
fchmod(11, 0100600)                     = 0
fchmod(11, 0600)                        = 0
fcntl64(11, F_GETFL)                    = 0x2 (flags O_RDWR)
fstat64(11, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 
0) = 0xb6705000
_llseek(11, 0, [0], SEEK_CUR)           = 0
write(11, "[$Version]\nupdate_info=kded.upd:"..., 4096) = 4096
write(11, "ndow to Desktop 2=none\nWindow to"..., 1708) = 1708
fdatasync(11)                           = 0
close(11)                               = 0
munmap(0xb6705000, 4096)                = 0
rename("/home/bsamwel/.kde/share/config/kdeglobalsZbum9a.new", 
"/home/bsamwel/.kde/share/config/kdeglobals") = 0


So, here's my question: is that call to fdatasync() really necessary? 
And can it be disabled somehow? It makes laptop mode pretty much 
unusable on KDE. :-(


Basically, 
the way to reproduce this should be:

1. Install laptop-mode-tools, set ENABLE_LAPTOP_MODE_ON_AC=1 in 
laptop-mode.conf, and do /etc/init.d/laptop-mode reload.

2. Stop sysklogd.

3. Do "echo 1 > /proc/sys/vm/block_dump"

4. Use kwin without any necessary disk reads, and monitor dmesg.

If the bug still exists, you will see that kwin causes WRITE operations 
more than once every 10 minutes (the default write interval of 
laptop-mode-tools).

I once looked into the code, and I traced the problem to an fsync() or 
fdatasync() call in one of the file handler functions in the underlying 
KDE libraries. It was a sync call that was completely unnecessary and 
uncalled for, I think it was triggered when kwin tried to save its 
settings or something like that.

Another way to reproduce this: run kwin under strace, and check for 
fsync(), fdatasync() and sync() syscalls.

I hope you can fix this (if it still occurs), because it's really 
annoying for KDE users who use a laptop and who try to save battery 
power using laptop-mode-tools.

Cheers,
Bart