[K12OSN] Poor performance woes

Tue Sep 20 21:15:15 UTC 2011

Keep in mind that although apps run on the server, they still make use
of Xserver memory to load images. Xserver memory is on the client. It
is very easy to have apps crash a thin client because they overload
the available memory of the Xserver on the client. Swap can help
mitigate this. Also, you can try booting with the "nocompcache" kernel
parameter (added to your pxelinux.cfg/default file). It is debatable
as to whether the default use of compcache helps or hinders on low ram
clients.

-Gadi

On Tue, Sep 20, 2011 at 5:02 PM, Gideon Romm
<ltsp at symbio-technologies.com> wrote:
> That just tells you the service is on. If you don't have NBD_SWAP in
> your lts.conf, then you are not using it.
>
> I believe there is also a parameter to use local swap from a hard
> drive, though I don't recall. Perhaps check the docs. Otherwise, if I
> remember, I will look in the code.
>
> -Gadi
>
> On Tue, Sep 20, 2011 at 4:51 PM, Jomegat <jomegat at jomegat.com> wrote:
>> On 09/20/2011 04:36 PM, Gideon Romm wrote:
>>>
>>> Try enabling NBD_SWAP.  If the clients have insufficient RAM, the best
>>> you can do is add swap space and hope the OS will swap out something
>>> else.
>>
>> Thanks.  I've already got that enabled as best I can tell.  Here's a snippet
>> from chkconfig --list:
>>
>> xinetd based services:
>>  [snip]
>>        nbdrootd:       on
>>        nbdswapd:       on
>>
>> Maybe that's where the 21MiB/sec is coming from.
>>
>> As soon as I can get back to the school, I'll run top on the TC and see
>> what's going on.
>>
>> Would it be possible (or advisable) to run swap on the TC from a local HD
>> instead of over the network?
>>
>>>
>>> -Gadi
>>>
>>> On Tue, Sep 20, 2011 at 3:18 PM, Jomegat<jomegat at jomegat.com>  wrote:
>>>>
>>>> I have a K12Linux setup based on EL6-64.  The TC's are ancient i686's
>>>> with
>>>> 256M RAM and 10/100 nics.  The TS has a gigE NIC, and between the TS&
>>>>  TCs
>>>> is a managed switch with 2 gigE ports and 24 10/100 ports.  The TS is
>>>> connected via one of the gigE's.
>>>>
>>>> We have a student who is having real performance problems when he loads a
>>>> page.  I went in today to be there while he was experiencing woe, and ran
>>>> the system monitor applet.
>>>>
>>>> When he loads the web page - with no flash in it that I can find - the
>>>> network maxes out at 12MiB/sec, and it takes an eternity for the page to
>>>> load.  He reports that sometimes this particular page will cause the TC
>>>> to
>>>> crash (black screen with text followed by login screen), but he was not
>>>> able
>>>> to reproduce that while I was there.  I suspect there is some user error
>>>> involved in the crash scenario, but it will be difficult to prove.
>>>>
>>>> I had tried running firefox as a local app last month, but the school
>>>> needs
>>>> flash, and it requires 512M.  Performance on these TC's was substantially
>>>> worse when running FF as a local app, so I backed off of that.
>>>>
>>>> The page he was trying to load is password protected, but I had him
>>>> ctrl-U
>>>> while he had it open, and save the source to a file which I can share if
>>>> need be.  It is filled with javascript, but I'm not sure that's the
>>>> culprit
>>>> (though it seems the most likely suspect).  I found no .flv, FLV, .swf,
>>>> or
>>>> .SWF in the file anywhere.
>>>>
>>>> As an experiment, I connected a monitor, keybd, and mouse directly to the
>>>> server and had him login there.  The page loads just fine that way.  That
>>>> might be a possible solution, but for some reason, the display is
>>>> incredibly
>>>> blurry.  If I make that permanent, I'd have to run some cable through the
>>>> wall (they're pinched in the door right now, and barely reach).
>>>>
>>>> Before they called me in to look at this, he had been bringing his mom's
>>>> laptop to school so he could do his work (it's an online course).  If it
>>>> crashes while he is taking a quiz, he loses a test attempt or gets a bad
>>>> grade, so this has to be reliable.
>>>>
>>>> His mom is on the school board, and she is pushing the school to abandon
>>>> LTSP in favor of a Windows solution.  They think that if they install
>>>> some
>>>> flavor of windows on the TC's they will get better performance, but I
>>>> believe they won't, as flash will need 512M no matter the OS.  I think
>>>> they
>>>> will need all new PC's if they go that route.
>>>>
>>>> I am on the cusp of losing my network to Windows, at which point I will
>>>> resign my post as unpaid volunteer sysadmin, so if I sound a little
>>>> desperate, now you know why.
>>>>
>>>> Any help here would be greatly appreciated.
>>>>
>>>> --
>>>> Jim Thomas            Principal Applications Engineer  Bittware, Inc
>>>> jthomas at bittware.com  http://www.bittware.com    (603) 226-0404 x536
>>>> The problem with the future is that it keeps turning into the present -
>>>> Hobbes
>>>>
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>>>>
>>>
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>>>
>>
>>
>> --
>> Jim Thomas            Principal Applications Engineer  Bittware, Inc
>> jthomas at bittware.com  http://www.bittware.com    (603) 226-0404 x536
>> The problem with the future is that it keeps turning into the present -
>> Hobbes
>>
>> _______________________________________________
>> K12OSN mailing list
>> K12OSN at redhat.com
>> https://www.redhat.com/mailman/listinfo/k12osn
>> For more info see <http://www.k12os.org>
>>
>