MPI2007 Flag Description
Intel Corporation Intel Server System R2208WFTZS (Intel Xeon Gold 6148, 2.40 GHz)
Copyright © 2013 Intel Corporation. All Rights Reserved.
Base Optimization Flags
-
- -O3
![[user]](http://www.spec.org/auto/mpi2007/flags/user.png)
- OPTIMIZE
-
Enables O2 optimizations plus more aggressive optimizations,
such as prefetching, scalar replacement, and loop and memory
access transformations. Enables optimizations for maximum speed,
such as:
- Loop unrolling, including instruction scheduling
- Code replication to eliminate branches
- Padding the size of certain power-of-two arrays to allow
more efficient cache use.
On IA-32 and Intel EM64T processors, when O3 is used with options
-ax or -x (Linux) or with options /Qax or /Qx (Windows), the compiler
performs more aggressive data dependency analysis than for O2, which
may result in longer compilation times.
The O3 optimizations may not cause higher performance unless loop and
memory access transformations take place. The optimizations may slow
down code in some cases compared to O2 optimizations.
The O3 option is recommended for applications that have loops that heavily
use floating-point calculations and process large data sets. On IA-32
Windows platforms, -O3 sets the following:
/GF (/Qvc7 and above), /Gf (/Qvc6 and below), and /Ob2
- Includes:
-
- -xCORE-AVX512
- OPTIMIZE
-
May generate Intel(R) Advanced Vector Extensions 512
(Intel(R) AVX-512) Foundation instructions, Intel(R)
AVX-512 Conflict Detection instructions, Intel(R) AVX-512
Doubleword and Quadword instructions, Intel(R) AVX-512
Byte and Word instructions and Intel(R) AVX-512 Vector
Length Extensions for Intel(R) processors, and the
instructions enabled with CORE-AVX512.
-
- -no-prec-div
- OPTIMIZE
-
(disable/enable[default] -[no-]prec-div)
-prec-div improves precision of floating-point divides. It has a slight
impact on speed. -no-prec-div disables this option and enables
optimizations that give slightly less precise results than full IEEE
division.
When you specify -no-prec-div along with some optimizations, such as
-xN and -xB (Linux) or /QxN and /QxB (Windows),
the compiler may change floating-point division computations into multiplication
by the reciprocal of the denominator.
For example, A/B is computed as A * (1/B) to improve the speed of the
computation.
However, sometimes the value produced by this transformation is
not as accurate as full IEEE division. When it is important to have fully
precise IEEE division, do not use -no-prec-div which will enable the
default -prec-div and the result is more accurate, with some
loss of performance.
-
-
- -O3
- OPTIMIZE
-
Enables O2 optimizations plus more aggressive optimizations,
such as prefetching, scalar replacement, and loop and memory
access transformations. Enables optimizations for maximum speed,
such as:
- Loop unrolling, including instruction scheduling
- Code replication to eliminate branches
- Padding the size of certain power-of-two arrays to allow
more efficient cache use.
On IA-32 and Intel EM64T processors, when O3 is used with options
-ax or -x (Linux) or with options /Qax or /Qx (Windows), the compiler
performs more aggressive data dependency analysis than for O2, which
may result in longer compilation times.
The O3 optimizations may not cause higher performance unless loop and
memory access transformations take place. The optimizations may slow
down code in some cases compared to O2 optimizations.
The O3 option is recommended for applications that have loops that heavily
use floating-point calculations and process large data sets. On IA-32
Windows platforms, -O3 sets the following:
/GF (/Qvc7 and above), /Gf (/Qvc6 and below), and /Ob2
- Includes:
-
- -xCORE-AVX512
- OPTIMIZE
-
May generate Intel(R) Advanced Vector Extensions 512
(Intel(R) AVX-512) Foundation instructions, Intel(R)
AVX-512 Conflict Detection instructions, Intel(R) AVX-512
Doubleword and Quadword instructions, Intel(R) AVX-512
Byte and Word instructions and Intel(R) AVX-512 Vector
Length Extensions for Intel(R) processors, and the
instructions enabled with CORE-AVX512.
-
- -no-prec-div
- OPTIMIZE
-
(disable/enable[default] -[no-]prec-div)
-prec-div improves precision of floating-point divides. It has a slight
impact on speed. -no-prec-div disables this option and enables
optimizations that give slightly less precise results than full IEEE
division.
When you specify -no-prec-div along with some optimizations, such as
-xN and -xB (Linux) or /QxN and /QxB (Windows),
the compiler may change floating-point division computations into multiplication
by the reciprocal of the denominator.
For example, A/B is computed as A * (1/B) to improve the speed of the
computation.
However, sometimes the value produced by this transformation is
not as accurate as full IEEE division. When it is important to have fully
precise IEEE division, do not use -no-prec-div which will enable the
default -prec-div and the result is more accurate, with some
loss of performance.
-
-
- -O3
- OPTIMIZE
-
Enables O2 optimizations plus more aggressive optimizations,
such as prefetching, scalar replacement, and loop and memory
access transformations. Enables optimizations for maximum speed,
such as:
- Loop unrolling, including instruction scheduling
- Code replication to eliminate branches
- Padding the size of certain power-of-two arrays to allow
more efficient cache use.
On IA-32 and Intel EM64T processors, when O3 is used with options
-ax or -x (Linux) or with options /Qax or /Qx (Windows), the compiler
performs more aggressive data dependency analysis than for O2, which
may result in longer compilation times.
The O3 optimizations may not cause higher performance unless loop and
memory access transformations take place. The optimizations may slow
down code in some cases compared to O2 optimizations.
The O3 option is recommended for applications that have loops that heavily
use floating-point calculations and process large data sets. On IA-32
Windows platforms, -O3 sets the following:
/GF (/Qvc7 and above), /Gf (/Qvc6 and below), and /Ob2
- Includes:
-
- -xCORE-AVX512
- OPTIMIZE
-
May generate Intel(R) Advanced Vector Extensions 512
(Intel(R) AVX-512) Foundation instructions, Intel(R)
AVX-512 Conflict Detection instructions, Intel(R) AVX-512
Doubleword and Quadword instructions, Intel(R) AVX-512
Byte and Word instructions and Intel(R) AVX-512 Vector
Length Extensions for Intel(R) processors, and the
instructions enabled with CORE-AVX512.
-
- -no-prec-div
- OPTIMIZE
-
(disable/enable[default] -[no-]prec-div)
-prec-div improves precision of floating-point divides. It has a slight
impact on speed. -no-prec-div disables this option and enables
optimizations that give slightly less precise results than full IEEE
division.
When you specify -no-prec-div along with some optimizations, such as
-xN and -xB (Linux) or /QxN and /QxB (Windows),
the compiler may change floating-point division computations into multiplication
by the reciprocal of the denominator.
For example, A/B is computed as A * (1/B) to improve the speed of the
computation.
However, sometimes the value produced by this transformation is
not as accurate as full IEEE division. When it is important to have fully
precise IEEE division, do not use -no-prec-div which will enable the
default -prec-div and the result is more accurate, with some
loss of performance.
-
-
- -O3
- OPTIMIZE
-
Enables O2 optimizations plus more aggressive optimizations,
such as prefetching, scalar replacement, and loop and memory
access transformations. Enables optimizations for maximum speed,
such as:
- Loop unrolling, including instruction scheduling
- Code replication to eliminate branches
- Padding the size of certain power-of-two arrays to allow
more efficient cache use.
On IA-32 and Intel EM64T processors, when O3 is used with options
-ax or -x (Linux) or with options /Qax or /Qx (Windows), the compiler
performs more aggressive data dependency analysis than for O2, which
may result in longer compilation times.
The O3 optimizations may not cause higher performance unless loop and
memory access transformations take place. The optimizations may slow
down code in some cases compared to O2 optimizations.
The O3 option is recommended for applications that have loops that heavily
use floating-point calculations and process large data sets. On IA-32
Windows platforms, -O3 sets the following:
/GF (/Qvc7 and above), /Gf (/Qvc6 and below), and /Ob2
- Includes:
-
- -xCORE-AVX512
- OPTIMIZE
-
May generate Intel(R) Advanced Vector Extensions 512
(Intel(R) AVX-512) Foundation instructions, Intel(R)
AVX-512 Conflict Detection instructions, Intel(R) AVX-512
Doubleword and Quadword instructions, Intel(R) AVX-512
Byte and Word instructions and Intel(R) AVX-512 Vector
Length Extensions for Intel(R) processors, and the
instructions enabled with CORE-AVX512.
-
- -no-prec-div
- OPTIMIZE
-
(disable/enable[default] -[no-]prec-div)
-prec-div improves precision of floating-point divides. It has a slight
impact on speed. -no-prec-div disables this option and enables
optimizations that give slightly less precise results than full IEEE
division.
When you specify -no-prec-div along with some optimizations, such as
-xN and -xB (Linux) or /QxN and /QxB (Windows),
the compiler may change floating-point division computations into multiplication
by the reciprocal of the denominator.
For example, A/B is computed as A * (1/B) to improve the speed of the
computation.
However, sometimes the value produced by this transformation is
not as accurate as full IEEE division. When it is important to have fully
precise IEEE division, do not use -no-prec-div which will enable the
default -prec-div and the result is more accurate, with some
loss of performance.
-
Implicitly Included Flags
This section contains descriptions of flags that were included implicitly
by other flags, but which do not have a permanent home at SPEC.
-
-
-
- -Ob_n
-
Specifies the level of inline function expansion.
Ob0 - Disables inlining of user-defined functions. Note that
statement functions are always inlined.
Ob1 - Enables inlining when an inline keyword or an inline
attribute is specified. Also enables inlining according
to the C++ language.
Ob2 - Enables inlining of any function at the compiler's
discretion.
-
- -O2
-
Enables optimizations for speed. This is the generally recommended
optimization level. This option also enables:
- Inlining of intrinsics
- Intra-file interprocedural optimizations, which include:
- inlining
- constant propagation
- forward substitution
- routine attribute propagation
- variable address-taken analysis
- dead static function elimination
- removal of unreferenced variables
- The following capabilities for performance gain:
- constant propagation
- copy propagation
- dead-code elimination
- global register allocation
- global instruction scheduling and control speculation
- loop unrolling
- optimized code selection
- partial redundancy elimination
- strength reduction/induction variable simplification
- variable renaming
- exception handling optimizations
- tail recursions
- peephole optimizations
- structure assignment lowering and optimizations
- dead store elimination
On IA-32 Windows platforms, -O2 sets the following:
/Og, /Oi-, /Os, /Oy, /Ob2, /GF (/Qvc7 and above), /Gf (/Qvc6
and below), /Gs, and /Gy.
- Includes:
-
-
-
-
-
-
-
- -O1
-
Enables optimizations for speed and disables some optimizations that
increase code size and affect speed.
To limit code size, this option:
- Enables global optimization; this includes data-flow analysis,
code motion, strength reduction and test replacement, split-lifetime
analysis, and instruction scheduling.
- Disables intrinsic recognition and intrinsics inlining.
The O1 option may improve performance for applications with very large
code size, many branches, and execution time not dominated by code within loops.
On IA-32 Windows platforms, -O1 sets the following:
/Qunroll0, /Oi-, /Op-, /Oy, /Gy, /Os, /GF (/Qvc7 and above),
/Gf (/Qvc6 and below), /Ob2, and /Og
- Includes:
-
-
Intel(R) MPI Library 2017 for Linux* options and environment variables
Job startup command flags
-n <# of processes> or -np <# of processes>
Use this option to set the number of MPI processes to run the current arg-set.
-perhost <# of processes> or -ppn <# of processes>
Use this option to place the indicated number of consecutive
MPI processes on every host in group round robin fashion. The number
of processes to start is controlled by the option -n as usual.
-genv <ENVVAR> <value>
Use this option to set the <ENVVAR> environment variable
to the specified <value> for all MPI processes.
Environment variables
I_MPI_FABRICS=<fabric>|<intra-node fabric>:<inter-node fabric>
Select the particular network fabric to be used.
tmi - Tag Matching Interface (TMI)-capable network fabrics, such as Intel True Scale Fabric and
Myrinet* (through TMI).
shm - Shared-memory only
dapl - Direct Access Programming Library* (DAPL)-capable network fabrics, such as InfiniBand* and
iWarp* (through DAPL)
ofi - OpenFabrics Interfaces* (OFI)-capable network fabrics, such as Intel True Scale Fabric and
Ethernet (through OFI API).
I_MPI_FALLBACK=<0|1>
Set this environment variable to enable fallback to the available
fabric. It is valid only for rdssm and rdma modes.
Fall back to the shared memory and/or socket fabrics
if initialization of the DAPL* fabric fails.
This is the default value.
Terminate the job if the fabric selected by the I_MPI_DEVICE
environment variable cannot be initialized.
I_MPI_COMPATIBILITY=<value>
Available values:
3 - The Intel MPI Library 3.x compatible mode
4 - The Intel MPI Library 4.0.x compatible mode
Set this environment variable to choose the Intel MPI Library runtime compatible mode. By default, the library
complies with the MPI-3.1 standard.
I_MPI_HYDRA_PMI_CONNECT=<value>
Available values:
nocache - Do not cache PMI messages
cache - Cache PMI messages on the local pmi_proxy management processes to minimize the number of PMI requests. Cached information is automatically propagated to child management processes
lazy-cache - cache mode with on-demand propagation. This is the default value.
alltoall - Information is automatically exchanged between all pmi_proxy before any get request can bedone.
Define the processing method for PMI messages.
For questions about the meanings of these flags, please contact the tester.
For other inquiries, please contact webmaster@spec.org
Copyright 2006-2010 Standard Performance Evaluation Corporation
Tested with SPEC MPI2007 v2.0.1.
Report generated on Tue Aug 22 18:38:22 2017 by SPEC MPI2007 flags formatter v1445.
![[benchmark]](http://www.spec.org/auto/mpi2007/flags/benchmark.png)
![[suite]](http://www.spec.org/auto/mpi2007/flags/suite.png)