OMP2012 Flag Description
Lenovo Global Technology ThinkSystem SR860 V2
Copyright © 2012 Intel Corporation. All Rights Reserved.
Base Optimization Flags
-
- -O3
![[user]](http://www.spec.org/auto/omp2012/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
-
Code is optimized for Intel(R) processors with support for AVX512 instructions.
The resulting code may contain unconditional use of features that are not supported
on other processors. This option also enables new optimizations in addition to
Intel processor-specific optimizations including advanced data layout and code
restructuring optimizations to improve memory accesses for Intel processors.
Do not use this option if you are executing a program on a processor that
is not an Intel processor. If you use this option on a non-compatible processor
to compile the main program (in Fortran) or the function main() in C/C++, the
program will display a fatal run-time error if they are executed on unsupported
processors.
-
-
- -fp-model fast=2
- OPTIMIZE
-
enable floating point model variation
[no-]except - enable/disable floating point semantics
fast[=1|2] - enables more aggressive floating point optimizations
precise - allows value-safe optimizations
source - enables intermediates in source precision
strict - enables -fp-model precise -fp-model except, disables
contractions and enables pragma stdc fenv_access
double - rounds intermediates in 53-bit (double) precision
extended - rounds intermediates in 64-bit (extended) precision
-
-
-
- -qopt-zmm-usage=high
- OPTIMIZE
-
Defines a level of zmm registers usage.
-qopt-zmm-usage=keywoard Specifies the level of zmm register usage. You can specify one of the following:
low - Tells the compiler that the compiled program is unlikely to benefit from zmm register usage. It specifies that the compiler should avoid using zmm register unless it can prove the gain from their usage.
high - Tells the compiler to generate zmm code without restrictions
-
-
- -fomit-frame-pointer
- OPTIMIZE
-
Determines whether EBP is used as a general-purpose register in optimizations.
EBP is used as a general-purpose register in optimizations. However, on Linux* and macOS* systems, the default is -fno-omit-frame-pointer
Option -fomit-frame-pointer allows this use.
-
-
-
- -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
-
Code is optimized for Intel(R) processors with support for AVX512 instructions.
The resulting code may contain unconditional use of features that are not supported
on other processors. This option also enables new optimizations in addition to
Intel processor-specific optimizations including advanced data layout and code
restructuring optimizations to improve memory accesses for Intel processors.
Do not use this option if you are executing a program on a processor that
is not an Intel processor. If you use this option on a non-compatible processor
to compile the main program (in Fortran) or the function main() in C/C++, the
program will display a fatal run-time error if they are executed on unsupported
processors.
-
-
- -fp-model fast=2
- OPTIMIZE
-
enable floating point model variation
[no-]except - enable/disable floating point semantics
fast[=1|2] - enables more aggressive floating point optimizations
precise - allows value-safe optimizations
source - enables intermediates in source precision
strict - enables -fp-model precise -fp-model except, disables
contractions and enables pragma stdc fenv_access
double - rounds intermediates in 53-bit (double) precision
extended - rounds intermediates in 64-bit (extended) precision
-
-
-
- -qopt-zmm-usage=high
- OPTIMIZE
-
Defines a level of zmm registers usage.
-qopt-zmm-usage=keywoard Specifies the level of zmm register usage. You can specify one of the following:
low - Tells the compiler that the compiled program is unlikely to benefit from zmm register usage. It specifies that the compiler should avoid using zmm register unless it can prove the gain from their usage.
high - Tells the compiler to generate zmm code without restrictions
-
-
- -fomit-frame-pointer
- OPTIMIZE
-
Determines whether EBP is used as a general-purpose register in optimizations.
EBP is used as a general-purpose register in optimizations. However, on Linux* and macOS* systems, the default is -fno-omit-frame-pointer
Option -fomit-frame-pointer allows this use.
-
-
-
- -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
-
Code is optimized for Intel(R) processors with support for AVX512 instructions.
The resulting code may contain unconditional use of features that are not supported
on other processors. This option also enables new optimizations in addition to
Intel processor-specific optimizations including advanced data layout and code
restructuring optimizations to improve memory accesses for Intel processors.
Do not use this option if you are executing a program on a processor that
is not an Intel processor. If you use this option on a non-compatible processor
to compile the main program (in Fortran) or the function main() in C/C++, the
program will display a fatal run-time error if they are executed on unsupported
processors.
-
-
- -fp-model fast=2
- OPTIMIZE
-
enable floating point model variation
[no-]except - enable/disable floating point semantics
fast[=1|2] - enables more aggressive floating point optimizations
precise - allows value-safe optimizations
source - enables intermediates in source precision
strict - enables -fp-model precise -fp-model except, disables
contractions and enables pragma stdc fenv_access
double - rounds intermediates in 53-bit (double) precision
extended - rounds intermediates in 64-bit (extended) precision
-
-
-
- -qopt-zmm-usage=high
- OPTIMIZE
-
Defines a level of zmm registers usage.
-qopt-zmm-usage=keywoard Specifies the level of zmm register usage. You can specify one of the following:
low - Tells the compiler that the compiled program is unlikely to benefit from zmm register usage. It specifies that the compiler should avoid using zmm register unless it can prove the gain from their usage.
high - Tells the compiler to generate zmm code without restrictions
-
-
- -fomit-frame-pointer
- OPTIMIZE
-
Determines whether EBP is used as a general-purpose register in optimizations.
EBP is used as a general-purpose register in optimizations. However, on Linux* and macOS* systems, the default is -fno-omit-frame-pointer
Option -fomit-frame-pointer allows this use.
-
- -align array64byte
- FOPTIMIZE
-
specify how data items are aligned
keywords: all (same as -align), none (same as -noalign),
[no]commons, [no]dcommons,
[no]qcommons, [no]zcommons,
rec1byte, rec2byte, rec4byte,
rec8byte, rec16byte, rec32byte,
array8byte, array16byte, array32byte,
array64byte, array128byte, array256byte,
[no]records, [no]sequence
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:
-
-
KMP_AFFINITY
The KMP_AFFINITY environment variable uses the following general syntax:
Syntax
|
|
KMP_AFFINITY=[<modifier>,...]<type>[,<permute>][,<offset>]
|
For example, to list a machine topology map, specify KMP_AFFINITY=verbose,none to use a modifier of verbose and a type of none.
The following table describes the supported specific arguments.
| Argument |
Default
|
Description
|
|
modifier
|
noverbose
respect
granularity=core
|
Optional. String consisting of keyword and specifier.
|
|
type
|
none
|
Required string. Indicates the thread affinity to use.
-
compact
-
disabled
-
explicit
-
none
-
scatter
-
logical (deprecated; instead use compact, but omit any permute value)
-
physical (deprecated; instead use scatter, possibly with an offset value)
The logical and physical types are deprecated but supported for backward compatibility.
|
|
permute
|
0
|
Optional. Positive integer value. Not valid with type values of explicit, none, or disabled. |
|
offset
|
0
|
Optional. Positive integer value. Not valid with type values of explicit, none, or disabled.
|
Affinity Types
Type is the only required argument.
type = none (default)
Does not bind OpenMP threads to particular thread contexts; however, if the operating system supports affinity, the compiler still uses the OpenMP thread affinity interface to determine machine topology. Specify KMP_AFFINITY=verbose,none to list a machine topology map.
type = compact
Specifying compact assigns the OpenMP thread <n>+1 to a free thread context as close as possible to the thread context where the <n> OpenMP thread was placed. For example, in a topology map, the nearer a node is to the root, the more significance the node has when sorting the threads.
type = disabled
Specifying disabled completely disables the thread affinity interfaces. This forces the OpenMP run-time library to behave as if the affinity interface was not supported by the operating system. This includes the low-level API interfaces such as kmp_set_affinity and kmp_get_affinity, which have no effect and will return a nonzero error code.
type = explicit
Specifying explicit assigns OpenMP threads to a list of OS proc IDs that have been explicitly specified by using the proclist= modifier, which is required for this affinity type.
type = scatter
Specifying scatter distributes the threads as evenly as possible across the entire system. scatter is the opposite of compact; so the leaves of the node are most significant when sorting through the machine topology map.
Deprecated Types: logical and physical
Types logical and physical are deprecated and may become unsupported in a future release. Both are supported for backward compatibility.
For logical and physical affinity types, a single trailing integer is interpreted as an offset specifier instead of a permute specifier. In contrast, with compact and scatter types, a single trailing integer is interpreted as a permute specifier.
Specifying logical assigns OpenMP threads to consecutive logical processors, which are also called hardware thread contexts. The type is equivalent to compact, except that the permute specifier is not allowed. Thus, KMP_AFFINITY=logical,n is equivalent to KMP_AFFINITY=compact,0,n (this equivalence is true regardless of the whether or not a granularity=fine modifier is present).
Permute and offset combinations
For both compact and scatter, permute and offset are allowed; however, if you specify only one integer, the compiler interprets the value as a permute specifier. Both permute and offset default to 0.
The permute specifier controls which levels are most significant when sorting the machine topology map. A value for permute forces the mappings to make the specified number of most significant levels of the sort the least significant, and it inverts the order of significance. The root node of the tree is not considered a separate level for the sort operations.
The offset specifier indicates the starting position for thread assignment.
Modifier Values for Affinity Types
Modifiers are optional arguments that precede type. If you do not specify a modifier, the noverbose, respect, and granularity=core modifiers are used automatically.
Modifiers are interpreted in order from left to right, and can negate each other. For example, specifying KMP_AFFINITY=verbose,noverbose,scatter is therefore equivalent to setting KMP_AFFINITY=noverbose,scatter, or just KMP_AFFINITY=scatter.
modifier = noverbose (default)
Does not print verbose messages.
modifier = verbose
Prints messages concerning the supported affinity. The messages include information about the number of packages, number of cores in each package, number of thread contexts for each core, and OpenMP thread bindings to physical thread contexts.
Information about binding OpenMP threads to physical thread contexts is indirectly shown in the form of the mappings between hardware thread contexts and the operating system (OS) processor (proc) IDs. The affinity mask for each OpenMP thread is printed as a set of OS processor IDs.
KMP_LIBRARY
KMP_LIBRARY = { throughput | turnaround | serial },
Selects the OpenMP run-time library execution mode.
The options for the variable value are throughput, turnaround, and serial.
Execution modes
The compiler with OpenMP enables you to run an application under different
execution modes that can be specified at run time. The libraries support
the serial, turnaround, and throughput modes.
Serial
The serial mode forces parallel applications to run on a single processor.
Turnaround
In a dedicated (batch or single user) parallel environment where all
processors are exclusively allocated to the program for its entire run,
it is most important to effectively utilize all of the processors all
of the time. The turnaround mode is designed to keep active all of the
processors involved in the parallel computation in order to minimize the
execution time of a single job. In this mode, the worker threads actively
wait for more parallel work, without yielding to other threads.
Avoid over-allocating system resources. This
occurs if either too many threads have been specified, or if too few processors
are available at run time. If system resources are over-allocated, this
mode will cause poor performance. The throughput mode should be used instead
if this occurs.
Throughput
In a multi-user environment where the load on the parallel machine is
not constant or where the job stream is not predictable, it may be better
to design and tune for throughput. This minimizes the total time to run
multiple jobs simultaneously. In this mode, the worker threads will yield
to other threads while waiting for more parallel work.
The throughput mode is designed to make the program aware of its environment
(that is, the system load) and to adjust its resource usage to produce
efficient execution in a dynamic environment. This mode is the default.
KMP_BLOCKTIME
KMP_BLOCKTIME = value.
Sets the time, in milliseconds, that a thread should wait, after completing
the execution of a parallel region, before sleeping.Use the optional
character suffixes: s (seconds), m (minutes), h (hours), or d (days)
to specify the units.Specify infinite for an unlimited wait time.
KMP_STACKSIZE
KMP_STACKSIZE = value.
Sets the number of bytes to allocate for each OpenMP* thread
to use as the private stack for the thread.
Recommended size is 16m.
Use the optional suffixes: b (bytes), k (kilobytes), m (megabytes),
g (gigabytes), or t (terabytes) to specify the units.
This variable does not affect the native operating system threads
created by the user program nor the thread executing the sequential
part of an OpenMP* program or parallel programs created using -parallel.
OMP_NUM_THREADS
Sets the maximum number of threads to use for OpenMP* parallel regions if no
other value is specified in the application. This environment variable
applies to both -openmp and -parallel.
Example syntax on a Linux system with 8 cores:
export OMP_NUM_THREADS=8
OMP_DYNAMIC
OMP_DYNAMIC={ 1 | 0 }
Enables (1, true) or disables (0,false) the dynamic adjustment of the number of threads.
OMP_SCHEDULE
OMP_SCHEDULE={ type,[chunk size]}
Controls the scheduling of the for-loop work-sharing construct.
type can be either of static,dynamic,guided,runtime
chunk size should be positive integer
OMP_NESTED
OMP_NESTED={ 1 | 0 }
Enables creation of new teams in case of nested parallel regions (1,true) or serializes (0,false) all nested parallel regions. Default is 0.
For questions about the meanings of these flags, please contact the tester.
For other inquiries, please contact webmaster@spec.org
Copyright 2012-2020 Standard Performance Evaluation Corporation
Tested with SPEC OMP2012 v1.1.
Report generated on Wed Oct 14 09:42:29 2020 by SPEC OMP2012 flags formatter v538.
![[suite]](http://www.spec.org/auto/omp2012/flags/suite.png)
![[benchmark]](http://www.spec.org/auto/omp2012/flags/benchmark.png)