Heavy I/O blocks FreeBSD box for several seconds

Adrian Chadd adrian at freebsd.org
Wed Jul 6 16:49:54 UTC 2011

Has anyone re-run those IO benchmarks?

Something smells fishy there.. (with the benchmarking.)


2011/7/6 O. Hartmann <ohartman at zedat.fu-berlin.de>:
> On 07/06/11 12:37, arrowdodger wrote:
>> 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.
> I read about issues with the old codebase of X11 in FreeBSD's ports used,
> which could be the cause of some performance problems, but I wouldn't expect
> those I/O-triggered blockings on boxes without any GUI.
> I saw Linux very often performing tremendously better when used as a
> workstation or desktop, but this is often gained on the costs of other
> subsystems. I followed a very hard-to-understand discussion about grouping
> threads related to ttys which seems to get higher priorized in Linux to make
> the GUI more fluent, but this is definitely on cost of other subsystems,
> which in consequence gets less priorized.
> But even without GUI, Linux seems to perform I/O much better on
> multicore-/multiprocessor boxes than FreeBSD *.X and 9.X).
> Today I looked at some benchmarks performed by Phoronix/openbenchmark.org
> (http://www.phoronix.com/scan.php?page=article&item=freebsd8_ubuntu910&num=9)
> and it seems that threaded I/O is an issue in FreeBSD (compared to Linux). I
> have no glue how to "tune" those bottlenecks away in FBSD.
> I use SCHED_ULE on all machines, since it is supposed to be performing
> better on multicore boxes, but there are lots of suggestions switching back
> to the old SCHED_4BSD scheduler.
> Oliver
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