[Qemu-devel] does ext4 cause problems? (not data loss)

[Joseph Miller]

I have the latest version of Ubuntu, Jaunty, and I have converted my fs to
ext4.  Attempting to run a qcow image of WinXP Pro, backed by a qcow
image, on 0.10.3, even with kernel-kqemu is near impossible.  Commands:

#!/bin/sh

export QEMU_AUDIO_DRV=sdl
export SDL_VIDEODRVER=dga
sudo chmod 666 /dev/kqemu
/opt/qemu-0.10.3/bin/qemu -L /opt/qemu-0.10.3/share/qemu/ -kernel-kqemu
-hda winxp-200905.qcow -m 512 -usbdevice tablet -localtime -net
nic,model=rtl8139 -net user -soundhw sb16 -redir tcp:103389::3389

My host computer spends most of its time doing disk writes and my guest is
impossible to use.  The computer begins to boot, requests re-activation
(which I deny until I can get this straightened out) and then runs
slooooowly.  It does run, but I don't know why it is so slow.  One of the
reasons I upgraded to ext4 was to enjoy better Qemu performance.

I have instead created a sparse file and formatted it with reiserfs (which
on my crappy laptop gives very good qemu performance) and mounted it as a
loop filesystem.  Performance returns as expected and massive disk writing
ceases.

Anyone know what's up here?  Please CC me as I'm not on the list.  Thanks.

-Joseph

P.S. - just to feed a flame war, I still think BKL is a minor drawback for
the *vast* majority of regular users and ext4 is not as good as reiserfs,
especially for reading (where my disk spends most of its time).