On Sep 9, 2010, at 4:31 PM, Ashley Pittman wrote:
>> What is the exact semantics of an asynchronous barrier,
>
> I'm not sure of the exact semantics but once you've got your head around the
> concept it's fairly simple to understand how to use it, you call
> MPI_IBarrier() and it gives you a ha
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users-boun...@open-mpi.org wrote on 09/10/2010 10:27:02 AM:
> [image removed]
>
> Re: [OMPI users] MPI_Reduce performance
>
> Eugene Loh
>
> to:
>
> Open MPI Users
>
> 09/10/2010 10:30 AM
>
> Sent by:
&
Richard Treumann wrote:
Hi Ashley
I understand the problem with
descriptor
flooding can be serious in an application with unidirectional data
dependancy.
Perhaps we have a different perception of how common that is.
Ashley speculated it was a "significant minority." I don't know
logy Group
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users-boun...@open-mpi.org wrote on 09/09/2010 05:34:15 PM:
> [image removed]
>
> Re: [OMPI users] MPI_Reduce performance
>
> Ashley Pittman
>
>
because of
different speed of execution on different nodes, delays, etc...
If you account for this, you get the result I mentioned.
Alex
- Original Message -
From: Eugene Loh
To: Open MPI Users
Sent: Thursday, September 09, 2010 11:32 PM
Subject: Re: [OMPI users] MPI_Reduce
On 9 Sep 2010, at 21:40, Richard Treumann wrote:
>
> Ashley
>
> Can you provide an example of a situation in which these semantically
> redundant barriers help?
I'm not making the case for semantically redundant barriers, I'm making a case
for implicit synchronisation in every iteration of
Ashley
Can you provide an example of a situation in which these semantically
redundant barriers help?
I may be missing something but my statement for the text book would be
"If adding a barrier to your MPI program makes it run faster, there is
almost certainly a flaw in it that is better solv
On 9 Sep 2010, at 21:10, jody wrote:
> Hi
> @Ashley:
> What is the exact semantics of an asynchronous barrier,
I'm not sure of the exact semantics but once you've got your head around the
concept it's fairly simple to understand how to use it, you call MPI_IBarrier()
and it gives you a handle
Hi
@Ashley:
What is the exact semantics of an asynchronous barrier,
and is it part of the MPI specs?
Thanks
Jody
On Thu, Sep 9, 2010 at 9:34 PM, Ashley Pittman wrote:
>
> On 9 Sep 2010, at 17:00, Gus Correa wrote:
>
>> Hello All
>>
>> Gabrielle's question, Ashley's recipe, and Dick Treutmann's
On 9 Sep 2010, at 17:00, Gus Correa wrote:
> Hello All
>
> Gabrielle's question, Ashley's recipe, and Dick Treutmann's cautionary words,
> may be part of a larger context of load balance, or not?
>
> Would Ashley's recipe of sporadic barriers be a silver bullet to
> improve load imbalance prob
Alex A. Granovsky wrote:
Isn't in
evident from the theory of random processes and probability theory that in the limit of infinitely
large cluster and parallel process, the probability of deadlocks with current implementation is unfortunately
quite a finite quantity and in
n any
particular details of the program.
Just my two cents.
Alex Granovsky
- Original Message -
From: Richard Treumann
To: Open MPI Users
Sent: Thursday, September 09, 2010 10:10 PM
Subject: Re: [OMPI users] MPI_Reduce performance
I was pointing out that most programs have
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From:
Eugene Loh
To:
Open MPI Users
List-Post: users@lists.open-mpi.org
Date:
09/09/2010 12:40 PM
Subject:
Re: [OMPI users] MPI_Reduce performance
Sent by:
users-boun...@open-mpi.org
Gus Co
Gus Correa wrote:
More often than not some components lag behind (regardless of how
much you tune the number of processors assigned to each component),
slowing down the whole scheme.
The coupler must sit and wait for that late component,
the other components must sit and wait for the coupler,
an
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From: Ashley Pittman
To: Open MPI Users
Date: 09/09/2010 03:53 AM
Subject:Re: [OMPI users] MPI_Re
ogy Group
Dept X2ZA / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601
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From:
Ashley Pittman
To:
Open MPI Users
List-Post: users@lists.open-mpi.org
Date:
09/09/2010 03:53 AM
Subject:
Re: [OMPI users] MPI_Reduce performance
Sent by:
users-bou
On Sep 9, 2010, at 1:46 AM, Ashley Pittman wrote:
>
> On 9 Sep 2010, at 08:31, Terry Frankcombe wrote:
>
>> On Thu, 2010-09-09 at 01:24 -0600, Ralph Castain wrote:
>>> As people have said, these time values are to be expected. All they
>>> reflect is the time difference spent in reduce waiting
On 9 Sep 2010, at 08:31, Terry Frankcombe wrote:
> On Thu, 2010-09-09 at 01:24 -0600, Ralph Castain wrote:
>> As people have said, these time values are to be expected. All they
>> reflect is the time difference spent in reduce waiting for the slowest
>> process to catch up to everyone else. The
Yes Terry,
thats' right.
2010/9/9 Terry Frankcombe
> On Thu, 2010-09-09 at 01:24 -0600, Ralph Castain wrote:
> > As people have said, these time values are to be expected. All they
> > reflect is the time difference spent in reduce waiting for the slowest
> > process to catch up to everyone els
Mm,I don't understand.
The experiments on my appliciation shows that an intensive use of Barrier+
Reduce is more faster than a single Reduce.
2010/9/9 Ralph Castain
> As people have said, these time values are to be expected. All they reflect
> is the time difference spent in reduce waiting for
On Thu, 2010-09-09 at 01:24 -0600, Ralph Castain wrote:
> As people have said, these time values are to be expected. All they
> reflect is the time difference spent in reduce waiting for the slowest
> process to catch up to everyone else. The barrier removes that factor
> by forcing all processes t
As people have said, these time values are to be expected. All they reflect is
the time difference spent in reduce waiting for the slowest process to catch up
to everyone else. The barrier removes that factor by forcing all processes to
start from the same place.
No mystery here - just a reflec
More in depth,
total execution time without Barrier is about 1 sec.
Total execution time with Barrier+Reduce is 9453, with 128 procs.
2010/9/9 Terry Frankcombe
> Gabriele,
>
> Can you clarify... those timings are what is reported for the reduction
> call specifically, not the total executi
Hy Terry,
this time is spent in MPI_Reduce, it isn't total execution time.
2010/9/9 Terry Frankcombe
> Gabriele,
>
> Can you clarify... those timings are what is reported for the reduction
> call specifically, not the total execution time?
>
> If so, then the difference is, to a first approxima
Gabriele,
Can you clarify... those timings are what is reported for the reduction
call specifically, not the total execution time?
If so, then the difference is, to a first approximation, the time you
spend sitting idly by doing absolutely nothing waiting at the barrier.
Ciao
Terry
--
Dr. Ter
On 8 Sep 2010, at 10:21, Gabriele Fatigati wrote:
> So, im my opinion, it is better put MPI_Barrier before any MPI_Reduce to
> mitigate "asynchronous" behaviour of MPI_Reduce in OpenMPI. I suspect the
> same for others collective communications. Someone can explaine me why
> MPI_reduce has this
Doing Reduce without Barrier first allows one process to call Reduce and
exit immediately without waiting for other processes to call Reduce.
Therefore, this allows one process to advance faster than other processes.
I suspect the 2671 second result is the difference between the fastest and
slowest
Dear OpenMPI users,
i'm using OpenMPI 1.3.3 on Infiniband 4x interconnnection network. My
parallel application use intensive MPI_Reduce communication over
communicator created with MPI_Comm_split.
I've noted strange behaviour during execution. My code is instrumented with
Scalasca 1.3 to report s
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