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.
Operating Modes (Default=Custom Mode):
Operating Mode is a BIOS setting which allows you to select the appropriate mode of operation based on the specific user environment. This menu option is provided to allow optimization of the system for minimum power usage, maximum efficiency, or maximum performance.
Values for this BIOS setting can be:
Linux Huge Page settings
In order to take advantage of large pages, your system must be configured to use large pages. To configure your system for huge pages perform the following steps:
Note that further information about huge pages may be found in your Linux documentation file: /usr/src/linux/Documentation/vm/hugetlbpage.txt
HUGETLB_MORECORE
Set this environment variable to "yes" to enable applications to use large pages.
LD_PRELOAD=/usr/lib64/libhugetlbfs.so
Setting this environment variable is necessary to enable applications to use large pages.
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 Prefetch:
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 Sector Prefetch:
This BIOS option allows the enabling/disabling of a processor mechanism to fetch the adjacent cache line within an 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.
Power C-States:
Enabling the CPU States causes the CPU to enter a low-power mode when the CPU is idle.
Turbo Mode:
Enabling turbo mode can boost the overall CPU performance when all CPU cores are not being fully utilized.
Turbo Boost:
This BIOS option can be set to Power Optimized or Traditional. When Power Optimized is selected, Intel Turbo Boost Technology engages after Performance state P0 is sustained for longer than two seconds. When Traditional is selected, Intel Turbo Boost Technology is engaged even for P0 requests less than two seconds.
Demand Scrub:
Demand scrub occurs when the memory controller reads memory for data or instructions and the demand scrubbing logic detects a correctable error. Correct data is forwarded to the memory controller and written to memory. With demand scrubbing disabled, the data being read into the memory controller will be corrected by the ECC logic but no write to main memory occurs. Since the data is not corrected in memory, subsequent reads to the same will need to be corrected.
Zone Reclaim:
Zone reclaim allows the reclaiming of pages from a zone if the number of free pages falls below a watermark even if other zones still have enough pages available. Reclaiming a page can be more beneficial than taking the performance penalties that are associated with allocating a page on a remote zone, especially for NUMA machines.
High Bandwidth:
Enabling this option allows the chipset to defer memory transactions and process them out of order for optimal performance.
Data Reuse (Enable/Disable):
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.
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 effect 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";