[sf-lug] GNU Denemo chokes a dual core 2 GB server at the school

Kristian Erik Hermansen kristian.hermansen at gmail.com
Tue Sep 25 01:55:42 PDT 2007

I implemented Edubuntu at my University on some older hardware.  I
would say that I was satisfied with it up until about 10 clients.
After that, you have to remember that all tasks are occurring on the
central server, not on the end-points.  If you would like to utilize
the hardware of the end-points, let me suggest using Diskless Remote
Boot Linux (DRBL) or LTSP in fat-client mode.  This will allow you to
offload the processing to the clients, and not the main server.  I
assume your are encountering a sharing problem with the sound device
between all the computers.  Remember that standard LTSP (Edubuntu)
only forwards the Xorg traffic to the clients via a secured
connection, and that all operations are happening on the central
server.  Thus, if one resource gets contention on the server, all
client swill degrade as well...


On 9/24/07, Christian Einfeldt <einfeldt at gmail.com> wrote:
> hi
> Here is the next issue for our public middle school project.  And it is
> actually part of a recurring theme, it seems:  why is our linux lab lagging,
> when most people think that it should be able to handle what we are throwing
> at it.  My question is fairly long to explain, but simple to summarize:  why
> are we experiencing delays in playing music compositions using GNU Denemo
> under Edubuntu over a GB network that should be performing better, and what
> can we do to solve the problem without spending any money?
> As most of you know from reading this list, I am a volunteer supporting a
> public middle school with FOSS.  We have a brand new dual core server with 2
> GB of RAM whose only purpose in life is to support 24 chubby clients running
> edubuntu.  The thin clients have at least 256 MB of RAM, and most of them
> have swap space on their hard drive also, although some of them are true
> thin clients in that the hd has no swap and is basically a vestige.  I am
> told that we have a gigabyte network.  The server feeds the signal to the
> first 18 clients through one GB switch, and then that switch feeds another
> identical switch with services about 6 more clients.
> Our problem is that when we use GNU Denemo to play the short little
> compositions that the students write in class, we can have only one student
> play his / her composition at a time or the system is choked, meaning that
> it lags.  More specifically, all of the students find that their GNOME
> desktops are almost completely non-responsive to the mouse.  The mouse still
> moves, but programs launch very slowly for about 5 mins, at which time the
> choke point is presumably cleared, and then one student can again play his /
> her composition.  It might be possible for, say, 2 students or maybe even
> three students to play their music; but we don't know where that stress
> point is.
> And, in some ways, it doesn't even make sense to slowly add students and
> have them play music, simply because some people who have heard of this
> problem in passing furrow their brow and say that we shouldn't be having
> these problems.
> We are, of course, going to be trying to get more RAM in the clients; and
> swap for all of the clients; and we have thought of running GNU Denomo
> natively on each of the clients by booting them as stand alone work
> stations.
> For those of you who are familiar with the school, you can stop reading
> here, because what follows is basic data about the school, and you probably
> don't need to read it again.
> >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
> This inner city school has absolutely no budget for a real tech support
> person, and all of the teachers already are at work by 6:50 a.m., and they
> usually stay until 6:30 p.m., and then each of the teachers is expected to
> be available to field phone calls at home until 8 p.m.  All of this might
> sound kind of drastic, but our students typically come to this school of 290
> students under-performing their grade level by 2 grade levels, but leave the
> school as 8th graders typically performing at or above grade level.
> Seventy-five (75%) of our students come from households below the federal
> poverty guidelines.  65% of our students are African American; 17% are
> Latino; 10% are Asian; and 8% are Caucasian.  Despite the life challenges
> facing our students, last year our students tested in first place (as a
> student body) based on standardized testing.  So this school is succeeding
> in many ways, but they are really struggling in terms of technology, and
> that is all because of funding shortfalls.
> Coincidentally, the students spend no time here on Windows boxes, except for
> occasionally random Internet browsing on a teacher's Windows box.  But that
> is the exception, because, as you can imagine, the teachers don't want the
> students accessing their computers.  So when the students are not in the
> lab, they are using PClinuxOS boxes in several of the classrooms to do their
> Internet research.
> Overall, this school is making miracles with no funding.  I am hoping to
> move the whole school to FOSS eventually, but of course there is still a lot
> of work to be done.  Thus far, the music teacher is fairly impressed with
> the ability of students to compose music on GNU Denemo, but she would just
> like to be able to have all of the students listen to their compositions at
> the same time.  Typically, these compositions are no more than, say, 6 or 10
> bars long, just enough to get the students familiar with the basics of
> scales, rests, note duration, tempo, beat, etc.  Just the basics.
> Thanks in advance for the help.
> --
> Christian Einfeldt,
> Producer, The Digital Tipping Point
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Kristian Erik Hermansen

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