[Barrelfish-users] Messages

[Tim Harris (RESEARCH)]

Hi Zeus,

Two possible things to check:


·         Are you using printf or debug_printf for output?  I'd suggest using the latter - it really goes out right away, so you can trust what you see :)


·         If it possible that the message handler is doing something that is causing a recursive call to event_dispatch?  (Actually, maybe this would be from within printf?)

Cheers,

Tim





From: zeus at aluzina.org [mailto:zeus at aluzina.org] On Behalf Of Zeus Gómez Marmolejo
Sent: 17 August 2011 15:31
To: Timothy Roscoe
Cc: barrelfish-users at lists.inf.ethz.ch; Tim Harris (RESEARCH)
Subject: Re: [Barrelfish-users] Messages

Hi,

I discovered another surprising thing. I'm calling the function messages_wait_and_handle_next() to wait and dispatch one message. Which in turn calls to event_dispatch(). According to the info I get on screen, sometimes it handles two messages before returning. This is strange.

I was inspecting the code and it's calling to get_next_event() which is supposed to handle only one event from the waitset. I don't understand this behavior, is this possible?
zeus.

El 17 de agosto de 2011 14:48, Zeus Gómez Marmolejo <zeus.gomez at bsc.es<mailto:zeus.gomez at bsc.es>> escribió:
Ok, I don't get any failures when sending messages, as I'm always checking with can_send(). Otherwise, I call the event_dispatch().

But now I'm sure that messages get reordered somehow. It's difficult to send the code as it's quite involved, but I filled the code with some printf. I'm using own implemented barriers using the barrelfish message passing and I see the message handler that is in the barrier dispatching messages that were sent after the barrier reply. Then suddenly the message reply for the barrier arrives ... how can it be?

I don't know how the stub is working but is it possible that is sending a retry of a message after the following message has been sent?

zeus.

El 13 de agosto de 2011 17:49, Timothy Roscoe <troscoe at inf.ethz.ch<mailto:troscoe at inf.ethz.ch>> escribió:


Well, messages should never be lost or reordered on a UMP channel, but
both sending and receiving messages can temporarily fail in a variety
of ways (we push retries due to full channels, etc. back to the
sender).

This means that a single-threaded sender and receiver can deadlock if
they're not careful about handling things like send failures due to a
full channel, or the need to send acks back from the receiver.

The stubs try to hide most of the functionality required for this,
except for the fact that any send or recv can fail (as with Unix NBIO
and select/poll).

That said, you probably already know most of this :-)

And, of course, there are probably bugs.

 -- Mothy

At Sat, 13 Aug 2011 15:08:27 +0200, Zeus Gómez Marmolejo <zeus.gomez at bsc.es<mailto:zeus.gomez at bsc.es>> wrote:
> I'm trying to simplify the code (I'm using all gasnet and the library I
> made), but whenever I get it simpler it turns out that it's working...
>
> So I have to figure out where the problem is.
>
>
> El 12 de agosto de 2011 11:43, Tim Harris (RESEARCH)
> <tharris at microsoft.com<mailto:tharris at microsoft.com>>escribió:
>
> >  Could you post some code examples?****
> >
> > ** **
> >
> > Cheers,****
> >
> > ** **
> >
> > Tim****
> >
> > ** **
> >
> > ** **
> >
> > ** **
> >
> > *From:* Zeus Gómez Marmolejo [mailto:zeus.gomez at bsc.es<mailto:zeus.gomez at bsc.es>]
> > *Sent:* 12 August 2011 10:42
> > *To:* barrelfish-users at lists.inf.ethz.ch<mailto:barrelfish-users at lists.inf.ethz.ch>
> > *Subject:* [Barrelfish-users] Messages****
> >
> > ** **
> >
> > Hi,****
> >
> > ** **
> >
> > I'm developing a benchmark for message passing in Barrelfish, but I don't
> > get it working properly. I experience some random errors. ****
> >
> > ** **
> >
> > The application is single threaded and it's using the flounder stubs to
> > send messages via the UMP backend. Some of the messages get lost. Is it
> > possible that they arrive in different order that they were sent? I'm not
> > sure how to debug it****
> >
> > ** **
> >
> > ** **
> >
> > Thanks for your help!
> >
> > --
> > Zeus Gómez Marmolejo
> > Barcelona Supercomputing Center
> > PhD student
> > http://www.bsc.es
> >
> > ****
> >
>
>
>
> --
> Zeus Gómez Marmolejo
> Barcelona Supercomputing Center
> PhD student
> http://www.bsc.es
>



--
Zeus Gómez Marmolejo
Barcelona Supercomputing Center
PhD student
http://www.bsc.es




--
Zeus Gómez Marmolejo
Barcelona Supercomputing Center
PhD student
http://www.bsc.es

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