Re: Poor desktop responsiveness with background I/O-operations

Thomas Fjellstrom
2009-09-20T04:11:16Z

On Sat September 19 2009, Ulrich Lukas wrote:
> 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)
>

I've seen similar things with my Intel p35 (q6600) system, especially under
64bit. Heavy i/o makes the rest of the system perform very badly. I have
however not noticed nearly as much of a problem with my AMD (SB700&SB750)
systems.

--
Thomas Fjellstrom
tfjellstrom@shaw.ca