ARSC T3D Users' Newsletter 13, December 2, 1994
Upcoming Software Upgrade on T3D
ARSC will be upgrading the T3D software to CrayLib_M 188.8.131.52, MAX 184.108.40.206 and SCC_M 220.127.116.11 on December 4th.
By now, users should have run their programs and saved the executables and results. These executables and results should be compared to the results after the new products are installed. If there are erroneous differences then Mike Ess should be contacted.
Using FLUSH to Keep I/O SynchronizedCoert Olmsted of ARSC brought in a puzzler that is illustrated by the following code and results:
cat writepenum.f intrinsic my_pe integer mype mype = my_pe() write(6,111) mype call barrier if(mype.eq.0) write(6,222) call barrier write(6,111) mype 111 format(1x,i2,$) 222 format(/) end /mpp/bin/cf77 writepenum.f a.out 2 2 4 4 3 3 7 7 5 5 6 6 1 1 0 0It was intended that the use of the format character "$" would prevent new lines from each PE to the screen output and there would be only two lines of output, with each line having each PE report once. What actually happens is that the writes are executing correctly, obeying the barrier calls but, each PE does writes to its own buffer which is then dumped to the screen when all the PEs terminate.
The solution to get the desired results is to not let results accumulate in the individual buffers but to flush them out at the right time. Now the source looks like:
intrinsic my_pe integer mype mype = my_pe() write(6,111) mype call flush( 6 ) call barrier() if(mype.eq.0) write(6,222) call barrier() write(6,111) mype call flush( 6 ) 111 format(1x,i2,$) 222 format(/) endand the expected results are:
7 0 5 4 2 6 1 3 0 1 4 2 6 5 7 3Using the FLUSH routine, the I/O buffers do not hide the order of events.
RemindersList of differences between T3D and Y-MP:
The current list of differences between the T3D and the Y-MP is:
- Data type sizes are not the same (Newsletter #5)
- Uninitialized variables are different (Newsletter #6)
- The effect of the -a static compiler switch (Newsletter #7)
- There is no GETENV on the T3D (Newsletter #8)
- Missing routine SMACH on T3D (Newsletter #9)
- Different Arithmetics (Newsletter #9)
- Different clock granularities for gettimeofday (Newsletter #11)
PE LimitsAt ARSC, most production runs can be handled by the 32 PE NQS queue. The use of large partitions of 64 or 128 PEs seems restricted to research problems of the "what if..." type. Basically, development is done on smaller partitions and then to complete a table of performance or problem sizes, the larger partitions are used.
We have been accommodating this situation by individually changing a user's interactive permissions with the understanding that users would share their results with us. We are in the process of notifying users of the change in this policy. In the future we will reset everyone back to the default settings and then make it easy for users to request changes that will be in effect for a short time period (perhaps a week per request).
Future NewsletterWhile at the past Supercomputing '94 conference I got a lot of information on the T3D. It will take me a while to outline it, but eventually you'll see all of it in the upcoming newsletters.
Supplemental Update - Sunday, Dec 4
Upcoming upgrade on ARSC T3D softwareARSC will be upgrading the T3D software to CrayLib_M 18.104.22.168, MAX 22.214.171.124 and SCC_M 126.96.36.199 in the near future.
We attempted this upgrade Sunday, December 4th, but were unsuccessful. We will try again in the near future and ARSC will notify its T3D users through this newsletter distribution when the upgrade is complete.
Second Call for Test ProgramsIn putting together a regression test for upgrades of T3D software, I found two areas where I need more coverage with user-supplied programs. I would like to ask again for users to submit test programs on:
- PVM called from Fortran
- Shmem routines called from either Fortran or C
Ed Kornkven ARSC HPC Specialist ph: 907-450-8669 Kate Hedstrom ARSC Oceanographic Specialist ph: 907-450-8678 Arctic Region Supercomputing Center University of Alaska Fairbanks PO Box 756020 Fairbanks AK 99775-6020
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