[Beowulf] PVM on wireless...

Robert G. Brown rgb at phy.duke.edu
Wed Feb 6 16:28:24 EST 2008


On Wed, 6 Feb 2008, Reuti wrote:

> Just an idea to check: PVM can also be started without rsh/ssh between the 
> machines. You have to copy and paste some things from here to there and back 
> and can startup all daemons this way by hand (page 30 in the PVM book). Maybe 
> this works - just to narrow the cause.

I'll look into this, thanks, although the daemon IS started -- the block
it is somewhere after that.  But it is well worth trying anyway.

I also wonder about ports and WAP interactions.  I've got my WAP
configured (AFAICT) as an internal switch, not really as a router.  As
in my laptop get DCHP service from my linux server, not the WAP, which
is flat to broadcasts, has no port filtering on the internal network
etc.

I even ran tcpdump on the problem last time it happened -- maybe I
should try it again.

    rgb

>
> -- Reuti
>
>
>> I suspect a race condition, probably caused by using raw UDP with some
>> assumption of latency during the handshake.  The one way I can think of
>> that the two connections differ is in their latency -- even the
>> bandwidth of wireless is every bit as great as 10B2 networks I've run
>> PVM on in years past (on proportionally slower CPUs, of course).  If the
>> master or slave send out an acknowledgement packet either before the
>> window where the other can receive it or after it has grown bored and
>> stopped listening, it might fail to properly bind or something.  It
>> seems like it would be a bug, not a feature, but if I were feeling
>> infinitely masochistic and were to wander down into Other People's
>> Source (ouch!) to try to debug this, that's what I'd look for first.
>> 
>> Any PVM developers still on list?  Any comments from them?
>>
>>   rgb
>> 
>>> 
>>> Just a thought,
>>> 
>>> -bill
>>> 
>>> 
>>> On Feb 6, 2008, at 10:40 AM, Robert G. Brown wrote:
>>> 
>>>> Anybody on list have any idea why PVM fails to add hosts over a wireless
>>>> link?  I've now tried this over multiple distro version and at least one
>>>> PVM update, and it just doesn't work.  Works fine over a wire, fails on
>>>> wireless, and as far as I know wire and wireless are both "identical"
>>>> at the kernel interface layer so that any e.g. socket one might open is
>>>> absolutely ecumenical about what the underlying hardware is (good old
>>>> ISO/OSI layering, right?).
>>> 
>> 
>> -- 
>> Robert G. Brown                            Phone(cell): 1-919-280-8443
>> Duke University Physics Dept, Box 90305
>> Durham, N.C. 27708-0305
>> Web: http://www.phy.duke.edu/~rgb
>> Book of Lilith Website: http://www.phy.duke.edu/~rgb/Lilith/Lilith.php
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-- 
Robert G. Brown                            Phone(cell): 1-919-280-8443
Duke University Physics Dept, Box 90305
Durham, N.C. 27708-0305
Web: http://www.phy.duke.edu/~rgb
Book of Lilith Website: http://www.phy.duke.edu/~rgb/Lilith/Lilith.php
Lulu Bookstore: http://stores.lulu.com/store.php?fAcctID=877977
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