SPEC CPU2006 Flag Description for the Intel(R) C++ and Fortran Compiler 11.1 for IA32 and Intel 64 applications

Copyright © 2006 Intel Corporation. All Rights Reserved.

Sections

Selecting one of the following will take you directly to that section:

Optimization Flags

Portability Flags

Compiler Flags

System and Other Tuning Information

Platform settings

One or more of the following settings may have been set. If so, the "General Notes" section of the report will say so; and you can read below to find out more about what these settings mean.

KMP_STACKSIZE

Specify stack size to be allocated for each thread.

KMP_AFFINITY

KMP_AFFINITY = < physical | logical >, starting-core-id
specifies the static mapping of user threads to physical cores. For example, if you have a system configured with 8 cores, OMP_NUM_THREADS=8 and KMP_AFFINITY=physical,0 then thread 0 will mapped to core 0, thread 1 will be mapped to core 1, and so on in a round-robin fashion.

KMP_AFFINITY = granularity=fine,scatter
The value for the environment variable KMP_AFFINITY affects how the threads from an auto-parallelized program are scheduled across processors.
Specifying granularity=fine selects the finest granularity level, causes each OpenMP thread to be bound to a single thread context.
This ensures that there is only one thread per core on cores supporting HyperThreading Technology
Specifying scatter distributes the threads as evenly as possible across the entire system.
Hence a combination of these two options, will spread the threads evenly across sockets, with one thread per physical core.

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 (Linux and Mac OS X) or /Qopenmp and /Qparallel (Windows). Example syntax on a Linux system with 8 cores: export OMP_NUM_THREADS=8

Hardware Prefetcher:

This BIOS option allows the enabling/disabling of a processor mechanism to prefetch data into the cache according to a pattern-recognition algorithm.

In some cases, setting this option to Disabled may improve performance. Users should only disable this option after performing application benchmarking to verify improved performance in their environment.

Adjacent Cache Line Prefetch:

This BIOS option allows the enabling/disabling of a processor mechanism to fetch the adjacent cache line within a 128-byte sector that contains the data needed due to a cache line miss.

In some cases, setting this option to Disabled may improve performance. Users should only disable this option after performing application benchmarking to verify improved performance in their environment.

Data Reuse Optimization:

Enabling this BIOS option reduces the frequency of L3 cache updates from L1.

This may improve performance by reducing the internal bandwidth consumed by constantly updating L1 cache lines in L3.

Since this results in more fetches to main memory, setting this option to Disabled may improve performance in some cases. Users should only disable this option after performing application benchmarking to verify improved performance in their environment.

Performance/Watt:

This BIOS option sets the turbo boost engagement after the maximum power state (P0).

If set to Traditional this will be less than 2 seconds to provide maximum performance, otherwise P0 restained for more than 2 seconds. This setting is able to set to "Traditional" or "Power Optimized" in BIOS. This default setting is "Power Optimized".

FSB High Bandwidth Optimization:

Enabling this option allows the chipset to defer memory transactions and process them out of order for optimal performance.

Hyper-Threading Technology:

Disabling Intel's Hyper-Threading Technology reduces the number of threads per core to 1. The default is Enabled; in this case each core provides additional resources for executing up to 2 threads in parallel.

Patrol Scrubbing:

This is a background activity initiated by the processor to seek out and fix memory errors. Patrol Scrub scans all of memory doing simulated "READs" while checking for ECC errors. If any ECC errors are detected during this process, they are logged as Patrol errors. Correctable errors are corrected and written back into memory. This mode is able to set to "Enable" or "Disable" in BIOS.

Memory Voltage:

If set to "Normal" the system supplies 1.5V in memory, otherwise the system supplies 1.35V in memory. This setting is able to set to "Low" or "Normal" in BIOS. This default setting is "Low".

NUMA configuration:

This BIOS option allows enabling/disabling the support of Non-Uniform Memory Access (NUMA). In NUMA mode, physical memory addresses are divided between nodes at a large grain and resource allocation tables describing this division are presented to the operating system.

For example, on a two-node system, if both nodes are configured with 6GB of memory, physical memory addresses 0 - 6GB-1 map to one node and addresses 6GB-12GB-1 map to the other node. To make use of this, the operating system needs to be NUMA-aware and can then try to optimize access to the processor's local memory.

In Non-NUMA mode(NUMA configuration set to disabled), the interleave can be configured across the CPUs. Non-NUMA mode may lead to more balanced but generally reduced performance for bandwidth-sensitive applications.

ulimit -s <n>

Sets the stack size to n kbytes, or unlimited to allow the stack size to grow without limit.

submit= MYMASK=`printf '0x%x' $((1<<$SPECCOPYNUM))`; /usr/bin/taskset $MYMASK $command

When running multiple copies of benchmarks, the SPEC config file feature submit is sometimes used to cause individual jobs to be bound to specific processors. This specific submit command is used for Linux. The description of the elements of the command are:

Using numactl to bind processes and memory to cores

For multi-copy runs or single copy runs on systems with multiple sockets, it is advantageous to bind a process to a particular core. Otherwise, the OS may arbitrarily move your process from one core to another. This can affect performance. To help, SPEC allows the use of a "submit" command where users can specify a utility to use to bind processes. We have found the utility 'numactl' to be the best choice.

numactl runs processes with a specific NUMA scheduling or memory placement policy. The policy is set for a command and inherited by all of its children. The numactl flag "--physcpubind" specifies which core(s) to bind the process. "-l" instructs numactl to keep a process memory on the local node while "-m" specifies which node(s) to place a process memory. For full details on using numactl, please refer to your Linux documentation, 'man numactl'

submit= $[top]/mysubmit.pl $SPECCOPYNUM "$command"

On Xeon 74xx series processors, some benchmarks at peak will run n/2 copies on a system with n logical processors. The mysubmit.pl script assigns each copy in such a way that no two copies will share an L2 cache, for optimal performance. The script looks in /proc/cpuinfo to come up with the list of cores that will satisfy this requirement. The source code is shown below.

Source ******************************************************************************************************


#!/usr/bin/perl
 
use strict;
use Cwd;
 
# The order in which we want copies to be bound to cores
# Copies: 0, 1, 2, 3
# Cores:  0, 1, 3, 6
 
my $rundir        = getcwd;
 
my $copynum = shift @ARGV;

my $i;
my $j;
my $tag;
my $num;
my $core;
my $numofcores; 

my @proc;
my @cores;

open(INPUT, "/proc/cpuinfo") or
   die "can't open /proc/cpuinfo\n"; 

#open(OUTPUT, "STDOUT");

# proc[i][0] = logical processor ID
# proc[i][1] = physical processor ID
# proc[i][2] = core ID

$i = 0;
$numofcores = 0;

while(<INPUT>)
{
  chop;
 
  ($tag, $num) = split(/\s+:\s+/, $_);


  if ($tag eq "processor") {
      $proc[$i][0] = $num;
  }

  if ($tag eq "physical id") {
      $proc[$i][1] = $num;
  }

  if ($tag eq "core id") {
      $proc[$i][2] = $num;
      $i++;
      $numofcores++;
  }
}

$i = 0;
$j = 0;

for $core (0, 4, 2, 1, 5, 3) {
  while ($i < $numofcores) {
     if ($proc[$i][2] == $core) {
        $cores[$j] = $proc[$i][0];
        $j++;
     }
     $i++;
  }
  $i=0;
}

open  RUNCOMMAND, "> runcommand" or die "failed to create run file";
print RUNCOMMAND "cd $rundir\n";
print RUNCOMMAND "@ARGV\n";
close RUNCOMMAND;
system 'taskset', '-c', $cores[$copynum], 'sh', "$rundir/runcommand";