[mpich-discuss] How to use non-blocking send/receive without calling MPI_Wait

[Lei Shi]

Pavan,

In my case, I don't care the data is correct or not. I know it sounds crazy
at first time, but there are some numerical schemes designed for this
situation.

I think according to Jeff's post
http://blogs.cisco.com/performance/dont-leak-mpi_requests. If we don't call
MPI_Wait or test, the request object will not be released even the data
transfer completes.

I will test your suggestion to call  MPI_Request_free to release
it manually.

BTW, attached is my test result,
1. The orange one uses MPI_ISend/MPI_IRecv with MPI_Wait to make sure the
data has been received successfully.  The WTime is linear with iterations,
which is correct.

2. The blue one uses MPI_ISend and MPI_IRecv without calling MPI_Wait.
There are some jumps in WTime. Does it due to some resource leaking? I will
try to call MPI_Request_free to solve those jumps.

3. The green one uses MPI_IBsend and MPI_IRecv (should I use MPI_Recv with
MPI_IBsend) without calling MPI_Wait. It is even slower than the case 1
with MPI_Wait.




On Fri, Apr 3, 2015 at 1:29 PM, Balaji, Pavan <balaji at anl.gov> wrote:

>
> No, the request object will get released fine when the data transfer
> completes.  It is a correct program.  What I meant is that, since the
> application never knows when the request completes, the user application
> cannot use the data in any meaningful way, IMO.
>
>   -- Pavan
>
> > On Apr 3, 2015, at 12:13 PM, Lei Shi <lshi at ku.edu> wrote:
> >
> > Pavan,
> >
> > Thanks. You mean since I don't call MPI_Wait at all, the request object
> does not get a chance to be released by the MPI library? Right? I will give
> it a try. Thanks again!
> >
> >
> > On Fri, Apr 3, 2015 at 10:12 AM, Balaji, Pavan <balaji at anl.gov> wrote:
> >
> > You can free the request with MPI_Request_free if you don't want to wait
> on it.  I have no idea how you'll write a correct program without waiting
> for receive completions at least, though.
> >
> >   -- Pavan
> >
> > > On Apr 2, 2015, at 11:44 PM, Lei Shi <lshi at ku.edu> wrote:
> > >
> > > Hi Junchao,
> > >
> > > Thanks for your reply. For my case, I don't want to check the data
> have been received or not. So I don't want to call MPI_Test or any function
> to verify it. But my problem is like if I ignore calling the MPI_Wait, just
> call Isend/Irev, my program freezes for several sec and then continues to
> run. My guess is probably I messed up the MPI library internal buffer by
> doing this.
> > >
> > >
> > > On Thu, Apr 2, 2015 at 7:25 PM, Junchao Zhang <jczhang at mcs.anl.gov>
> wrote:
> > > Does MPI_Test fit your needs?
> > >
> > > --Junchao Zhang
> > >
> > > On Thu, Apr 2, 2015 at 7:16 PM, Lei Shi <lshi at ku.edu> wrote:
> > > I want to use non-blocking send/rev MPI_Isend/MPI_Irev to do
> communication. But in my case, I don't really care what kind of data I get
> or it is ready to use or not. So I don't want to waste my time to do any
> synchronization  by calling MPI_Wait or etc API.
> > >
> > > But when I avoid calling MPI_Wait, my program is freezed several secs
> after running some iterations (after multiple MPI_Isend/Irev callings),
> then continues. It takes even more time than the case with MPI_Wait.  So my
> question is how to do a "true" non-blocking communication without waiting
> for the data ready or not. Thanks.
> > >
> > >
> > > _______________________________________________
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> > >
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> > > _______________________________________________
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> >
> > --
> > Pavan Balaji  ✉️
> > http://www.mcs.anl.gov/~balaji
> >
> > _______________________________________________
> > discuss mailing list     discuss at mpich.org
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> >
>
> --
> Pavan Balaji  ✉️
> http://www.mcs.anl.gov/~balaji
>
>
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