TTY task group scheduling

Lucius Windschuh lwindschuh at
Thu Nov 18 23:23:09 UTC 2010

2010/11/18 Bruce Cran <bruce at>:
>Have you tried increasing kern.sched.preempt_thresh? According to
>a good value for desktop use would be 224.

Hmm, I though I tried this -- but this helps indeed. :-)
The browser, movie player etc. behave much better when a "make -j4
buildworld" is running on my 2-core machine in the background. Thank

2010/11/18 Bruce Cran <bruce at>:
> If you're using UFS, I've found it to be quite a bottleneck when
> doing parallel IO: I even ran a "svn up" in one terminal and tried to
> login on another a couple of days ago only to find the motd took over 5
> seconds to appear! That may be excessive since I was running a kernel
> with WITNESS and INVARIANTS, but I've found ZFS to be far better if you
> want good interactivity when reading/writing to disks.

This is indeed another issue, which I also encountered, but explicitly
left out since I don't blame the task scheduler for that. ;)

Unfortunately, I don't know how much SCHED_ULE's inability to cope
with more runnable threads than cores, as Steve mentioned, accounts to
the problem I observe. Time to switch back to SCHED_4BSD? *sigh*


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