Heavy I/O blocks FreeBSD box for several seconds

[Andriy Gapon]

on 06/07/2011 13:37 arrowdodger said the following:
> 2011/7/6 O. Hartmann <ohartman at zedat.fu-berlin.de>
> 
>> When performing an update on the ports tree via "portsnap fetch update" or
>> when checking out (or) large Subversion repositories or when copying large
>> data files (~ 50 to 250 GB in size, results from numerical modelings) or
>> when compiling world, FreeBD 9.0 and FreeBSD 8.2-STABLE tend to "freeze" for
>> several seconds or drop overall performance dramatically for seconds. On
>> boxes with only console- or terminal access (no GUI) a running 'vi' gets
>> stuck for seconds while one of the processes producing heavy I/O is running,
>> or the output of a 'cat' of a large file stops for several seconds.
>>
>> Using X11, this phenomenon gets even worse and the 'freezing' tends to
>> persist sometimes for more than 10 or 15 seconds.
>>
> 
> I've also had (and still having) this problem on FreeBSD 7.2-RELEASE and
> 8-STABLE with both UFS and ZFS. Though, i've been running FreeBSD not on
> powerful servers, but on laptops (2-core CPU's, 2 GB of RAM). But still,
> KDE4 on Linux performs much better during high disk IO.


Just curious what your current value of sysctl kern.sched.preempt_thresh is.
And if it's not 224 and if you haven't tried 224 yet, then could you please try
it and see if there is any improvement?

This assumes that you use SCHED_ULE (kern.sched.name is "ULE").

-- 
Andriy Gapon