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From: Murat Knecht (murat.knecht_at_[hidden])
Date: 2007-10-23 14:10:04


Good to know that I'm not just not finding the solution, there simply is
none.
The system is actually dedicated to the job. But the process may, while
working, receive a signal that alters the ongoing job. Like for example
a terminate signal or more data to be taken into consideration. That's
why I need to listen in parallel and a CPU core less troublesome.
Thanks,
Murat

George Bosilca schrieb:
> Currently there is no work around this issue. We consider(ed) that
> when you run an MPI job the cluster is in dedicated mode, so a 100%
> CPU consumption is acceptable. However, as we discussed at our last
> meeting, there are others reasons to be able to yield the CPU until a
> message arrives. Therefore, we plan to have a blocking mode in the
> near future. The is no timeframe for this, but the discussions already
> started (that is usually a good sign).
>
> Thanks,
> george.
>
> On Oct 23, 2007, at 9:17 AM, Murat Knecht wrote:
>
>> Hi,
>> thanks for answering. Unfortunately, I did try that, too. The point
>> is that i don't understand the ressource consumption. Even if the
>> processor is yielded, it still is busy waiting, wasting system
>> resources which could otherwise be used for actual work. Isn't there
>> some way to activate an interrupt mechanism, so that the wait/recv
>> blocks the thread, e.g. puts it to sleep, until notified?
>>
>> Murat
>>
>> Tim Mattox schrieb:
>>> You should look at these two FAQ entries:
>>> http://www.open-mpi.org/faq/?category=running#oversubscribing
>>> http://www.open-mpi.org/faq/?category=running#force-aggressive-degraded
>>> To get what you want, you need to force Open MPI to yield the
>>> processor rather than be aggressively waiting for a message. On
>>> 10/23/07, Murat Knecht <murat.knecht_at_[hidden]> wrote:
>>>> Hi, Testing a distributed system locally, I couldn't help but
>>>> notice that a blocking MPI_Recv causes 100% CPU load. I deactivated
>>>> (at both compile- and run-time) the shared memory bt-layer, and
>>>> specified "tcp, self" to be used. Still one core busy. Even on a
>>>> distributed system I intend to perform work, while waiting for
>>>> incoming requests. For this purpose having one core busy waiting
>>>> for requests is uncomfortable to say the least. Does OpenMPI not
>>>> use some blocking system call to a tcp port internally? Since i
>>>> deactivated the understandably costly shared-memory waits, this
>>>> seems weird to me. Someone has an explanation or even better a fix
>>>> / workaround / solution ? thanks, Murat
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