Date: Wed, 6 Jul 2011 13:33:37 +0000 From: Alexander Best <arundel@freebsd.org> To: arrowdodger <6yearold@gmail.com> Cc: FreeBSD Current <freebsd-current@freebsd.org>, freebsd-questions@freebsd.org Subject: Re: Heavy I/O blocks FreeBSD box for several seconds Message-ID: <20110706133337.GA89910@freebsd.org> In-Reply-To: <CALH631=F4bSgNDE4w0qcXGMgGxZRRwCP9n-H4M0c%2B1UEaqWr7Q@mail.gmail.com> References: <4E1421D9.7080808@zedat.fu-berlin.de> <CALH631=F4bSgNDE4w0qcXGMgGxZRRwCP9n-H4M0c%2B1UEaqWr7Q@mail.gmail.com>
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On Wed Jul 6 11, arrowdodger wrote: > 2011/7/6 O. Hartmann <ohartman@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. this might be a scheduling issue. iirc i/o intensive tasks have higher priority than cpu intensive tasks, because they are expected to only issue a i/o request and then free the processor, while cpu intensive tasks occupy the cpu a lot longer. so maybe a process whith cyclic i/o requests blocks processes which aren't doing i/o. maybe playing with ULE's options can improve the situation. since you're running GENERIC, preemption *should* be enabled. however you should double check. i once tried running ULE without preemption and experienced exactly the same situation you described in your mail. for ULE preemption is pretty much mandatory. for the old 4bsd scheduler, running without preemtion doesn't really make that much of a difference, compared to running with preemption. you might also want to try enabling options IPI_PREEMPTION. no idea, if this improves your situation, though. cheers. alex > > > > 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.
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