[buildd-tools-devel] Unresponsive mouse in X when compiling with schroot

[Roger Leigh]

On Wed, Jul 22, 2009 at 03:10:07PM +0200, Helge Kreutzmann wrote:

[poor responsiveness]

> Is there any experience in your team what setting might cause this? Is
> there some way to "renice" the schroot (I don't mind longer
> compilation times) so that the load on the system is reduced hence
> keeping the mouse under X usable?

I can't say I've noticed this myself.  It's indicative of a high system
load, but it's not clear from your description what the cause is.

Could you provide your schroot configuration for the chroot in
question? (schroot --config -c <chroot>).

If it's an LVM snapshot and doing heavy writing, you might get the
snapshot copy-on-write device doing some work.  For other chroot
types, other than the chroot() call, the system should behave
*identically* to running the build outside the chroot.

To find the underlying cause, running top, iotop etc. to see what's
causing the high load would be useful.


Renicing is certainly possible.  In your configuration
  command-prefix=nice
should do the trick.  However, command-prefix was originally
written to just run a single command with no arguments--it
might well not support arguments (originally added to prefix
the command with linux32 prior to integrated personality support).

I will be happy to update command-prefix to accept multiple args.
Then you can get it to prefix your command with "nice -n <level>"

Since schroot runs setuid root, we can call nice(2) directly
before exec()ing the command.  We could add a nice=level parameter
to the configuration file.  That's also a simple change which I
would be happy to make.

Since renicing is really only working around the poor performance,
it would be great to find out in more detail what the underlying
cause is, so we can (if possible) address that directly.


Regards,
Roger

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