I got it. You're right, it might not related to MPI. I need to figure out
what's the possible reason for it.
Again, thanks for your help.
Linbao
On Thu, Oct 21, 2010 at 12:06 PM, Eugene Loh wrote:
> My main point was that, while what Jeff said about the short-comings of
> calling timers after
My main point was that, while what Jeff said about the short-comings of
calling timers after Barriers was true, I wanted to come in defense of
this timing strategy. Otherwise, I was just agreeing with him that it
seems implausible that commenting out B should influence the timing of
A, but I'm
Hi, Eugene,
You said:
" The bottom line here is that from a causal point of view it would seem
that B should not impact the timings. Presumably, some other variable is
actually responsible here."
Could you explain it in more details for the second sentence. Thanks a lot.
Linbao
On Thu, Oct 21,
Thanks a lot.
On Thu, Oct 21, 2010 at 9:21 AM, Jeff Squyres wrote:
> Ah. The original code snipit you sent was:
>
> MPI::COMM_WORLD.Barrier();
> if if(rank == master) t1 = clock();
> "code A";
> MPI::COMM_WORLD.Barrier();
> if if(rank == master) t2 = clock();
> "code B";
>
> Remember that the t
Jeff Squyres wrote:
Ah. The original code snipit you sent was:
MPI::COMM_WORLD.Barrier();
if(rank == master) t1 = clock();
"code A";
MPI::COMM_WORLD.Barrier();
if(rank == master) t2 = clock();
"code B";
Remember that the time that individual processes exit barrier is not guaranteed
to be uni
Ah. The original code snipit you sent was:
MPI::COMM_WORLD.Barrier();
if if(rank == master) t1 = clock();
"code A";
MPI::COMM_WORLD.Barrier();
if if(rank == master) t2 = clock();
"code B";
Remember that the time that individual processes exit barrier is not guaranteed
to be uniform (indeed, it
Thanks a lot for your reply. By commenting code B, I mean if I remove the
code B part, then the time spent on code A seems to run faster. I do have a
lot of communications in code B too. It involves 500 procs. I had thought
code B should have no effect on the time spent on code A if I use
MPI_Barri
Thanks for your suggestion. I am trying MPI_Wtime to see if there is any
difference.
Linbao
On Thu, Oct 21, 2010 at 1:37 AM, jody wrote:
> Hi
>
> I don't know the reason for the strange behaviour, but anyway,
> to measure time in an MPI application you should use MPI_Wtime(), not
> clock()
>
>
On Oct 20, 2010, at 5:51 PM, Storm Zhang wrote:
> I need to measure t2-t1 to see the time spent on the code A between these two
> MPI_Barriers. I notice that if I comment code B, the time seems much less the
> original time (almost half). How does it happen? What is a possible reason
> for it?
Hi
I don't know the reason for the strange behaviour, but anyway,
to measure time in an MPI application you should use MPI_Wtime(), not clock()
regards
jody
On Wed, Oct 20, 2010 at 11:51 PM, Storm Zhang wrote:
> Dear all,
>
> I got confused with my recent C++ MPI program's behavior. I have an
Dear all,
I got confused with my recent C++ MPI program's behavior. I have an MPI
program in which I use clock() to measure the time spent between to
MPI_Barrier, just like this:
MPI::COMM_WORLD.Barrier();
if if(rank == master) t1 = clock();
"code A";
MPI::COMM_WORLD.Barrier();
if if(rank == mas
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