Messages in this thread | | | Date | Sun, 20 Sep 2009 05:08:43 +0200 | From | Ulrich Lukas <> | Subject | Poor desktop responsiveness with background I/O-operations |
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Hi,
using a recent hard-/software setup, I observed that continuous read/write operations severely degrade the overall system responsiveness in typical desktop-PC use cases.
Merely doing write/read operations on a data volume leads to stuck text and mouse cursors, seconds-long delays for simple window-context switches in X11, dropouts in low-resolution video playback etc.
Test case: - 64-bit dual-core PC, SATA harddrive, plenty of free RAM - vanilla Linux 2.6.31, Kubuntu 9.10 packages, all software 64-bit
How to reproduce: - start KDE/GNOME-session - open a terminal window and do as a non-root user: dd if=/dev/zero of=/home/john-doe/testfile (or dd if=/home/john-doe/big-testfile of=/dev/null)
- a real use scenario would be a daily disk-backup or the simple extraction of a tarball containing slightly bigger files
Observation: - The system becomes _really_ slow as described above; unusable for any multimedia tasks.
- Using an encrypted (dm-crypt/LUKS) /home (e.g. on mobile computers) compounds the issue to a painful extent.
Possible culprits (I'm guessing) are the Linux I/O- or CPU scheduler.
I realize that a single heavyweight transfer slows down I/O for the corresponding transactions/processes/volumes etc.
But there needs to be a fair distribution of I/O or CPU time which leaves enough for other basic operations. And this doesn't seem to be the case with recent Linux versions.
On a side note, I've tried the BFS-patches (bfs-221 on 2.6.31): This yields significantly higher throughput when using disk encryption (50% improvement with dm-crypt/LUKS, 512 bit aes-xts-plain cipher mode). But with these patches, the responsiveness was even worse during my quick test. Switching to a text-mode console: several /minutes/ delay...
I'm attaching my .config for linux 2.6.31 (grep ^C and bzip2-ed)
[unhandled content-type:application/octet-stream] | |