Intel® MPI Library Developer Reference for Linux* OS

Developer Reference

  • 2020
  • 09/11/2020
  • Public Content
Contents

Environment Variables for Process Pinning

I_MPI_PIN
Turn on/off process pinning.
Syntax
I_MPI_PIN=
<arg>
Arguments
<arg>
Binary indicator
enable | yes | on | 1
Enable process pinning. This is the default value
disable | no | off | 0
Disable process pinning
Description
Set this environment variable to control the process pinning feature of the Intel® MPI Library.
Syntax
Arguments
Description
I_MPI_PIN_PROCESSOR_LIST (I_MPI_PIN_PROCS)
Define a processor subset and the mapping rules for MPI processes within this subset.
Syntax
I_MPI_PIN_PROCESSOR_LIST=
<value>
 
The environment variable value has the following syntax forms:
1.
<proclist>
2.
[
<procset>
][:[grain=
<grain>
][,shift=
<shift>
][,preoffset=
<preoffset>
][,postoffset=
<postoffset>
]
3.
[
<procset>
][:map=
<map>
]
The following paragraphs provide detail descriptions for the values of these syntax forms.
Note
The
postoffset
 keyword has
offset
 alias.
Note
The second form of the pinning procedure has three steps:
  1. Cyclic shift of the source processor list on
    preoffset*grain
     value.
  2. Round robin shift of the list derived on the first step on
    shift*grain
     value.
  3. Cyclic shift of the list derived on the second step on the
    postoffset*grain
     value.
Note
The
grain
,
shift
,
preoffset
, and
postoffset
 parameters have a unified definition style.
This environment variable is available for both Intel® and non-Intel microprocessors, but it may perform additional optimizations for Intel microprocessors than it performs for non-Intel microprocessors.
Syntax
I_MPI_PIN_PROCESSOR_LIST=
<proclist>
Arguments
<proclist>
A comma-separated list of logical processor numbers and/or ranges of processors. The process with the i-th rank is pinned to the i-th processor in the list. The number should not exceed the amount of processors on a node.
<l>
Processor with logical number
<l>
 .
<l>-<m>
Range of processors with logical numbers from
<l>
 to
<m>
 .
<k>,<l>-<m>
Processors
<k>
 , as well as
<l>
 through
<m>
 .
Syntax
I_MPI_PIN_PROCESSOR_LIST=[
<procset>
][:[grain=
<grain>
][,shift=
<shift>
][,preoffset=
<preoffset>
][,postoffset=
<postoffset>
]
Arguments
<procset>
Specify a processor subset based on the topological numeration. The default value is
allcores
.
all
All logical processors. Specify this subset to define the number of CPUs on a node.
allcores
All cores (physical CPUs). Specify this subset to define the number of cores on a node. This is the default value.
If Intel® Hyper-Threading Technology is disabled,
allcores
 equals to
all
.
allsocks
All packages/sockets. Specify this subset to define the number of sockets on a node.
 
<grain>
Specify the pinning granularity cell for a defined
<procset>
 . The minimal
<grain>
 value is a single element of the
<procset>
 . The maximal
<grain>
 value is the number of
<procset>
 elements in a socket. The
<grain>
 value must be a multiple of the
<procset>
 value. Otherwise, the minimal
<grain>
 value is assumed. The default value is the minimal
<grain>
 value.
<shift>
Specify the granularity of the round robin scheduling shift of the cells for the
<procset>
 .
<shift>
 is measured in the defined
<grain>
 units. The
<shift>
 value must be positive integer. Otherwise, no shift is performed. The default value is no shift, which is equal to
1
 normal increment.
<preoffset>
Specify the cyclic shift of the processor subset
<procset>
 defined before the round robin shifting on the
<preoffset>
 value. The value is measured in the defined
<grain>
 units. The
<preoffset>
 value must be non-negative integer. Otherwise, no shift is performed. The default value is no shift.
<postoffset>
Specify the cyclic shift of the processor subset
<procset>
 derived after round robin shifting on the
<postoffset>
 value. The value is measured in the defined
<grain>
 units. The
<postoffset>
 value must be non-negative integer. Otherwise no shift is performed. The default value is no shift.
The following table displays the values for
<grain>
,
<shift>
,
<preoffset>
, and
<postoffset>
 options:
<n>
Specify an explicit value of the corresponding parameters.
<n>
 is non-negative integer.
fine
Specify the minimal value of the corresponding parameter.
core
Specify the parameter value equal to the amount of the corresponding parameter units contained in one core.
cache1
Specify the parameter value equal to the amount of the corresponding parameter units that share an L1 cache.
cache2
Specify the parameter value equal to the amount of the corresponding parameter units that share an L2 cache.
cache3
Specify the parameter value equal to the amount of the corresponding parameter units that share an L3 cache.
cache
The largest value among
cache1
,
cache2
, and
cache3
.
socket | sock
Specify the parameter value equal to the amount of the corresponding parameter units contained in one physical package/socket.
half | mid
Specify the parameter value equal to
socket/2
.
third
Specify the parameter value equal to
socket/3
.
quarter
Specify the parameter value equal to
socket/4
.
octavo
Specify the parameter value equal to
socket/8
.
Syntax
I_MPI_PIN_PROCESSOR_LIST=[
<procset>
][:map=
<map>
]
Arguments
<map>
The mapping pattern used for process placement.
bunch
The processes are mapped as close as possible on the sockets.
scatter
The processes are mapped as remotely as possible so as not to share common resources: FSB, caches, and core.
spread
The processes are mapped consecutively with the possibility not to share common resources.
Description
Set the
I_MPI_PIN_PROCESSOR_LIST
 environment variable to define the processor placement. To avoid conflicts with different shell versions, the environment variable value may need to be enclosed in quotes.
Note
This environment variable is valid only if
I_MPI_PIN
 is enabled.
The
I_MPI_PIN_PROCESSOR_LIST
 environment variable has the following different syntax variants:
  • Explicit processor list. This comma-separated list is defined in terms of logical processor numbers. The relative node rank of a process is an index to the processor list such that the i-th process is pinned on i-th list member. This permits the definition of any process placement on the CPUs.
    For example, process mapping for
    I_MPI_PIN_PROCESSOR_LIST=p0,p1,p2,...,pn
     is as follows:
    Rank on a node
    0
    1
    2
    ...
    n-1
    N
    Logical CPU
    p0
    p1
    p2
    ...
    pn-1
    Pn
  • grain/shift/offset
     mapping. This method provides cyclic shift of a defined
    grain
     along the processor list with steps equal to
    shift*grain
     and a single shift on
    offset*grain
     at the end. This shifting action is repeated
    shift
     times.
    For example: grain = 2 logical processors, shift = 3 grains, offset = 0.
Legend:
gray
 - MPI process grains
A)
red
 - processor grains chosen on the 1
st
 pass
B)
cyan
 - processor grains chosen on the 2
nd
 pass
C)
green
 - processor grains chosen on the final 3
rd
 pass
D) Final map table ordered by MPI ranks
A)
0 1
 
 
2 3
 
 
...
2n-2 2n-1
 
 
0 1
2 3
4 5
6 7
8 9
10 11
...
6n-6 6n-5
6n-4 6n-3
6n-2 6n-1
B)
0 1
2n 2n+1
 
2 3
2n+2 2n+3
 
...
2n-2 2n-1
4n-2 4n-1
 
0 1
2 3
4 5
6 7
8 9
10 11
...
6n-6 6n-5
6n-4 6n-3
6n-2 6n-1
C)
0 1
2n 2n+1
4n 4n+1
2 3
2n+2 2n+3
4n+2 4n+3
...
2n-2 2n-1
4n-2 4n-1
6n-2 6n-1
0 1
2 3
4 5
6 7
8 9
10 11
...
6n-6 6n-5
6n-4 6n-3
6n-2 6n-1
D)
0 1
2 3
…
2n-2 2n-1
2n 2n+1
2n+2 2n+3
…
4n-2 4n-1
4n 4n+1
4n+2 4n+3
…
6n-2 6n-1
0 1
6 7
…
6n-6 6n-5
2 3
8 9
…
6n-4 6n-3
4 5
10 11
…
6n-2 6n-1
  • Predefined mapping scenario. In this case popular process pinning schemes are defined as keywords selectable at runtime. There are two such scenarios:
    bunch
     and
    scatter
    .
In the
bunch
 scenario the processes are mapped proportionally to sockets as closely as possible. This mapping makes sense for partial processor loading. In this case the number of processes is less than the number of processors.
In the
scatter
 scenario the processes are mapped as remotely as possible so as not to share common resources: FSB, caches, and cores.
In the example, there are two sockets, four cores per socket, one logical CPU per core, and two cores per shared cache.
Legend:
gray
 - MPI processes
cy
an
 - 1
st
 socket processors
gre
en
 - 2
nd
 socket processors
Same color defines a processor pair sharing a cache
0
1
2
 
 
3
4
 
 
0
1
2
3
4
5
6
7
bunch
 scenario for 5 processes
0
4
2
6
 
1
5
3
7
0
1
2
3
4
5
6
7
scatter
 scenario for full loading
Examples
To pin the processes to CPU0 and CPU3 on each node globally, use the following command:

$ mpirun -genv I_MPI_PIN_PROCESSOR_LIST=0,3 -n <# of processes>
<executable>
To pin the processes to different CPUs on each node individually (CPU0 and CPU3 on host1 and CPU0, CPU1 and CPU3 on host2), use the following command:

$ mpirun -host host1 -env I_MPI_PIN_PROCESSOR_LIST=0,3 -n <# of processes> <executable> : \
-host host2 -env I_MPI_PIN_PROCESSOR_LIST=1,2,3 -n <# of processes> <executable>
To print extra debug information about process pinning, use the following command:

$ mpirun -genv I_MPI_DEBUG=4 -m -host host1 \
-env I_MPI_PIN_PROCESSOR_LIST=0,3 -n <# of processes> <executable> :\
-host host2 -env I_MPI_PIN_PROCESSOR_LIST=1,2,3 -n <# of processes> <executable>
Note
If the number of processes is greater than the number of CPUs used for pinning, the process list is wrapped around to the start of the processor list.
Examples
I_MPI_PIN_PROCESSOR_EXCLUDE_LIST
Define a subset of logical processors to be excluded for the pinning capability on the intended hosts.
Syntax
I_MPI_PIN_PROCESSOR_EXCLUDE_LIST=
<proclist>
Arguments
<proclist>
A comma-separated list of logical processor numbers and/or ranges of processors.
<l>
Processor with logical number
<l>
 .
<l>-<m>
Range of processors with logical numbers from
<l>
 to
<m>
 .
<k>,<l>-<m>
Processors
<k>
 , as well as
<l>
 through
<m>
 .
Description
Set this environment variable to define the logical processors that Intel® MPI Library does not use for pinning capability on the intended hosts. Logical processors are numbered as in
/proc/cpuinfo
.
I_MPI_PIN_CELL
Set this environment variable to define the pinning resolution granularity.
I_MPI_PIN_CELL
 specifies the minimal processor cell allocated when an MPI process is running.
Syntax
I_MPI_PIN_CELL=
<cell>
Arguments
<cell>
Specify the resolution granularity
unit
Basic processor unit (logical CPU)
core
Physical processor core
Description
Set this environment variable to define the processor subset used when a process is running. You can choose from two scenarios:
  • all possible CPUs in a node (
    unit
     value)
  • all cores in a node (
    core
     value)
The environment variable has effect on both pinning types:
  • one-to-one pinning through the
    I_MPI_PIN_PROCESSOR_LIST
     environment variable
  • one-to-many pinning through the
    I_MPI_PIN_DOMAIN
     environment variable
The default value rules are:
  • If you use
    I_MPI_PIN_DOMAIN
    , then the cell granularity is
    unit
    .
  • If you use
    I_MPI_PIN_PROCESSOR_LIST
    , then the following rules apply:
    • When the number of processes is greater than the number of cores, the cell granularity is
      unit
      .
    • When the number of processes is equal to or less than the number of cores, the cell granularity is
      core
      .
Note
The
core
 value is not affected by the enabling/disabling of Intel® Hyper-Threading Technology in a system.
I_MPI_PIN_RESPECT_CPUSET
Respect the process affinity mask.
Syntax
I_MPI_PIN_RESPECT_CPUSET=
<value>
Arguments
<value>
Binary indicator
enable | yes | on | 1
Respect the process affinity mask. This is the default value
disable | no | off | 0
Do not respect the process affinity mask
Description
If you set
I_MPI_PIN_RESPECT_CPUSET=enable
, the Hydra process launcher uses job manager's process affinity mask on each intended host to determine logical processors for applying Intel MPI Library pinning capability.
If you set
I_MPI_PIN_RESPECT_CPUSET=disable
, the Hydra process launcher uses its own process affinity mask to determine logical processors for applying Intel MPI Library pinning capability.
I_MPI_PIN_RESPECT_HCA
In the presence of Infiniband architecture* host channel adapter (IBA* HCA), adjust the pinning according to the location of IBA HCA.
Syntax
I_MPI_PIN_RESPECT_HCA=
<value>
Arguments
<value>
Binary indicator
enable | yes | on | 1
Use the location of IBA HCA if available. This is the default value
disable | no | off | 0
Do not use the location of IBA HCA
Description
If you set
I_MPI_PIN_RESPECT_HCA=enable
 , the Hydra process launcher uses the location of IBA HCA on each intended host for applying Intel MPI Library pinning capability.
If you set
I_MPI_PIN_RESPECT_HCA=disable
, the Hydra process launcher does not use the location of IBA HCA on each intended host for applying Intel MPI Library pinning capability.

Product and Performance Information

1

Intel's compilers may or may not optimize to the same degree for non-Intel microprocessors for optimizations that are not unique to Intel microprocessors. These optimizations include SSE2, SSE3, and SSSE3 instruction sets and other optimizations. Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel. Microprocessor-dependent optimizations in this product are intended for use with Intel microprocessors. Certain optimizations not specific to Intel microarchitecture are reserved for Intel microprocessors. Please refer to the applicable product User and Reference Guides for more information regarding the specific instruction sets covered by this notice.

Notice revision #20110804