BGQ
| Blue Gene/Q (BGQ) | |
|---|---|
| Installed | August 2012 |
| Operating System | RH6.2, CNK (Linux) |
| Number of Nodes | 2048(32,768 cores), 512 (8,192 cores) |
| Interconnect | 5D Torus (jobs), QDR Infiniband (I/O) |
| Ram/Node | 16 GB |
| Cores/Node | 16 (64 threads) |
| Login/Devel Node | bgqdev-fen1,bgq-fen1 |
| Vendor Compilers | bgxlc, bgxlf |
| Queue Submission | Loadleveler |
********** NOTE **********
This page is still under development and as such some of the information may not be current.
Support Email
Pleas use bgq-support@scinethpc.ca for BGQ specific inquiries.
Specifications
BGQ is an extremely dense and energy efficient 3rd generation blue gene IBM supercomputer built around a system on a chip compute node that has a 16core 1.6GHz PowerPC based CPU (PowerPC A2) with 16GB of Ram. The nodes are bundled in groups of 32 into a node board (512 cores), and 16 boards make up a midplane (8192 cores) with 2 midplanes per rack, or 16,348 cores and 16 GB of RAM per rack. The compute nodes run a very lightweight linux based operating system called CNK. The compute nodes are all connected together using a custom 5D torus highspeed interconnect. Each rack has 16 I/O nodes that run a full Redhat Linux OS that manages the compute nodes and mounts the filesystem. SciNet has 2 BGQ systems, a half rack 8192 core development system, and a 2 rack 32,768 core production system.
5D Torus Network
The network topology of Blue/Gene Q is a five-dimensional (5D) torus, with direct links between the nearest neighbors in the ±A, ±B, ±C, ±D, and ±E directions. As such there are only a few optimum block sizes that will use the network efficiently.
| Node Boards | Compute Nodes | Cores | Torus Dimensions |
| 1 | 32 | 512 | 2x2x2x2x2 |
| 2 (adjacent pairs) | 64 | 1024 | 2x2x4x2x2 |
| 4 (quadrants) | 128 | 2048 | 2x2x4x4x2 |
| 8 (halves) | 256 | 4096 | 4x2x4x4x2 |
| 16 (midplane) | 512 | 8192 | 4x4x4x4x2 |
| 32 (1 rack) | 1024 | 16384 | 4x4x4x8x2 |
| 64 (2 racks) | 2048 | 32768 | 4x4x8x8x2 |
Login/Devel Nodes
The development nodes for the BGQ are bgqdev-fen1 for the half-rack development system and bgq-fen1 for the 2-rack production system. You can login to them from the regular login.scinet.utoronto.ca login nodes or directly using, bgqdev.scinet.utoronto.ca. The nodes are IBM Power7 Linux which serve as compilation and submission hosts for the BGQ. Programs are cross-compiled for the BGQ on these nodes and then submitted to the queue using loadleveler.
Compilers
The BGQ uses IBM XL compilers to cross-compile code for the BGQ. Compilers are available for FORTRAN, C, and C++. The compilers by default produce static binaries, however with BGQ it is possible to now use dynamic libraries as well. The compilers follow the XL convections with the prefix bg, so bgxlc and bgxlf are the C and FORTRAN compilers respectively. Most users however will use the MPI variants which are shown below.
/bgsys/drivers/V1R1M1/ppc64/comm/xl/bin/mpich2version /bgsys/drivers/V1R1M1/ppc64/comm/xl/bin/mpixlc /bgsys/drivers/V1R1M1/ppc64/comm/xl/bin/mpixlf90
Job Submission
As the BGQ architecture is different from the development nodes, the only way to test your program is to submit a job to the BGQ. Jobs are submitted through loadleveler using runjob which in many ways similar to mpirun or mpiexec with a few BGQ specific flags. As shown above in the network topology overview, there are only a few optimum job size configurations which is also further constrained by each block requiring a minimum of one IO node. In SciNet's configuration (with 8 I/O nodes per midplane) this allows 64 nodes (1024 cores) to be the smallest block size. Typically a block size matches the job size to offer fully dedicated resources to the job. Multiple jobs can be run within the same block, however this results in shared resources (network and IO) and are referred to as sub-block jobs.
Loadleveler
Job submission is done through loadleveler with a few blue gene specific commands. The command "bg_shape" is in number of nodes, not cores, so a bg_shape=32 would be 512 cores.
#!/bin/sh # @ job_name = bgsample # @ job_type = bluegene # @ comment = "BGQ Job By Size" # @ error = $(job_name).$(Host).$(jobid).err # @ output = $(job_name).$(Host).$(jobid).out # @ bg_size = 32 # @ wall_clock_limit = 30:00 # @ bg_connectivity = Torus # @ queue # Launch all BGQ jobs using runjob runjob --cwd=$SCRATCH/ : $HOME/mycode.exe myflags
runjob
runjob on BGQ acts a lot like mpirun/mpiexec and is the launcher to start jobs on BGQ. The "block" argument is the predefined group of nodes that are already booted. See the next section on how to create these blocks manually. Note that a block does not need to be rebooted between jobs, only if the number of nodes or network parameters are need to be changed. For this example block R00-M0-N03-64 is made up of 2 node cards with 64 compute nodes (1024 cores).
runjob --block R00-M0-N03-64 --ranks-per-node=16 --np 1024 --cwd=$PWD : $PWD/code -f file.in
also the flag
--verbose #
where # is from 1-7 is very useful it you are trying to debug an application.
To run a sub-block job (ie share a block) you need to specify a "--corner" within the block to start the job and a 5D AxBxCxDxE "--shape". The following example shows 2 jobs sharing the same block.
runjob --block R00-M0-N03-64 --corner R00-M0-N03-J00 --shape 1x1x1x2x2 --ranks-per-node=16 --np 64 --cwd=$PWD : $PWD/code -f file.in runjob --block R00-M0-N03-64 --corner R00-M0-N03-J04 --shape 2x2x2x2x1 --ranks-per-node=16 --np 256 --cwd=$PWD : $PWD/code -f file.in
To see running jobs and the status of available blocks use on the service nodes:
list_jobs list_blocks
Filesystem
The BGQ has its own dedicated 500TB GPFS filesystem for both $HOME and $SCRATCH.
Documentation
BGQ System Administration Guide