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<!DOCTYPE flagsdescription SYSTEM "http://www.spec.org/dtd/cpuflags1.dtd">
<flagsdescription>
<filename>Bull-Intel-Platform-linux64-revC.xml</filename>
<title>SPEC CPU2006 Flag Description for Bull Intel-based systems</title>
<platform_settings>
<![CDATA[
<p><b>Platform settings</b></p>
<p>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.</p>
<p><b>Operating Modes (Default=Custom Mode):</b></p>
<p>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.</p>
<p>Values for this BIOS setting can be:</p>
<ul> <li><b>Acoustic/minimum power mode</b>: Strives to minimize the absolute power consumption of the system while it is operating.</li>
<li><b>Efficiency mode</b>: Maximizes the performance/watt efficiency as measured by power benchmarks. It provides the best features for reducing power and increasing performance without a detrimental effect on either one.</li>
<li><b>Performance mode</b>: Maximizes the absolute performance of the system by setting all programmable bus speeds to their maximum rated frequencies without regard for power.</li>
<li><b>Custom mode</b>: A combination of Efficiency mode and Performance mode.</li>
</ul>
<p><b>Linux Huge Page settings</b></p>
<p>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:</p>
<ul>
<li>Create a mount point for the huge pages: "mkdir /mnt/hugepages"</li>
<li>The huge page file system needs to be mounted when the systems reboots. Add the following to a system boot configuration file before any services are started: "mount -t hugetlbfs nodev /mnt/hugepages"</li>
<li>echo N > /proc/sys/vm/nr_hugepages, where N is the maximum number of pages the system may allocate.</li>
</ul>
<p>Note that further information about huge pages may be found in your Linux documentation file: /usr/src/linux/Documentation/vm/hugetlbpage.txt</p>
<p><b>Transparent Huge Pages</b></p>
<p>On RedHat EL 6 and later, Transparent Hugepages increase the memory page size from 4 kilobytes to 2 megabytes.
Transparent Hugepages provide significant performance advantages on systems with highly contended resources and large memory workloads.
If memory utilization is too high or memory is badly fragmented which prevents hugepages being allocated, the kernel will assign smaller
4k pages instead.
Hugepages are used by default if /sys/kernel/mm/redhat_transparent_hugepage/enabled is set to always.
</p>
<p><b>HUGETLB_MORECORE </b></p>
<p>
Set this environment variable to "yes" to enable applications to use large pages.
</p>
<p><b>LD_PRELOAD=/usr/lib64/libhugetlbfs.so </b></p>
<p>
Setting this environment variable is necessary to enable applications to use large pages.
</p>
<p><b>KMP_STACKSIZE </b></p>
<p>
Specify stack size to be allocated for each thread.
</p>
<p><b>KMP_AFFINITY </b></p>
<p>
KMP_AFFINITY = < physical | logical >, starting-core-id <br/>
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. <br/> </p>
<p>
KMP_AFFINITY = granularity=fine,scatter <br/>
The value for the environment variable KMP_AFFINITY affects how the threads from an auto-parallelized program are scheduled across processors. <br/>
Specifying granularity=fine selects the finest granularity level, causes each OpenMP thread to be bound to a single thread context. <br/>
This ensures that there is only one thread per core on cores supporting HyperThreading Technology<br/>
Specifying scatter distributes the threads as evenly as possible across the entire system. <br/>
Hence a combination of these two options, will spread the threads evenly across sockets, with one thread per physical core. <br/>
</p>
<p><b>OMP_NUM_THREADS </b></p>
<p>
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
</p>
<p><b>Intel(R) HT Technology:</b></p>
<p>
This BIOS setting enables/disables Intel's Hyper-Threading (HT) Technology. With HT Technology,
the operating system can execute two threads in parallel within each processor core.
</p>
<p><b>Hardware Prefetch:</b></p>
<p>
This BIOS option allows the enabling/disabling of a processor mechanism to
prefetch data into the cache according to a pattern-recognition algorithm.
</p>
<p>
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.
</p>
<p><b>Adjacent Cache Line Prefetch:</b></p>
<p>
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.
</p>
<p>
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.
</p>
<p><b>Data Reuse:</b></p>
<p>
This BIOS option allows the enabling/disabling of the Data Reuse optimization.
</p>
<p>
Enabling this option reduces the frequency of L3 cache updates from the L1 cache. This may improve performance
by reducing the internal bandwidth consumed by constantly updating L1 cache lines in the L3 cache.
</p>
<p>
Since this optimization results in more fetches to main memory, in some limited cases, setting this option to
Disabled may improve performance. In the majority of cases, the default value of Enabled provides better performance.
Users should only disable this option after performing application benchmarking to verify improved performance in
their environment.
</p>
<p><b>Intel(R) C-STATE tech:</b></p>
<p>
Enabling the CPU States causes the CPU to enter a low-power mode when the CPU
is idle.
</p>
<p><b>Intel(R) SpeedStep(tm) tech:</b></p>
<p>
Allow the clock speed of the processor to be dynamically changed (to different P-states) by software,This allows the
processor to meet the instantaneous performance needs of the operation being performed, while minimizing power draw and
heat dissipation.
</p>
<p><b>Intel(R) TurboMode tech:</b></p>
<p>
Enabling turbo mode can boost the overall CPU performance when all CPU cores are
not being fully utilized.
</p>
<p><b>Demand Scrubbing:</b></p>
<p>
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.
</p>
<p><b>Zone Reclaim:</b></p>
<p>
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.
</p>
<p><b>ulimit -s <n> </b></p>
<p>
Sets the stack size to <b>n</b> kbytes, or <b>unlimited</b> to allow the stack size
to grow without limit.
</p>
<p><b>submit= MYMASK=`printf '0x%x' $((1<<$SPECCOPYNUM))`; /usr/bin/taskset $MYMASK $command </b></p>
<p>When running multiple copies of benchmarks, the SPEC config file feature
<b>submit</b> is sometimes used to cause individual jobs to be bound to
specific processors. This specific submit command is used for Linux.
The description of the elements of the command are:</p>
<ul>
<li><b>/usr/bin/taskset [options] [mask] [pid | command [arg] ... ]</b>: <br/>
taskset is used to set or retreive the CPU affinity of a running
process given its PID or to launch a new COMMAND with a given CPU
affinity. The CPU affinity is represented as a bitmask, with the
lowest order bit corresponding to the first logical CPU and highest
order bit corresponding to the last logical CPU. When the taskset
returns, it is guaranteed that the given program has been scheduled
to a legal CPU.<br/>
The default behaviour of taskset is to run a new command with a
given affinity mask: <br/>
taskset [mask] [command] [arguments]</li>
<li><b>$MYMASK</b>: The bitmask (in hexadecimal) corresponding to a specific
SPECCOPYNUM. For example, $MYMASK value for the first copy of a
rate run will be 0x00000001, for the second copy of the rate will
be 0x00000002 etc. Thus, the first copy of the rate run will have a
CPU affinity of CPU0, the second copy will have the affinity CPU1
etc.</li>
<li><b>$command</b>: Program to be started, in this case, the benchmark instance
to be started.</li>
</ul>
<p><b>Using numactl to bind processes and memory to cores</b></p>
<p>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.</p>
<p>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'</p>
<p><b>numactl --interleave=all "runspec command" </b></p>
<p> Launching a process with numactl --interleave=all sets the memory interleave policy so that memory will be allocated using round robin on nodes. When memory cannot be allocated on the current interleave target fall back to other nodes.</p>
<p><b>Free the file system page cache</b></p>
<p>The command "echo 1> /proc/sys/vm/drop_caches" is used to free up the filesystem page cache.</p>
<p><b>submit= $[top]/mysubmit.pl $SPECCOPYNUM "$command" </b></p>
<p> 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.</p>
<p><b>Source</b><br />
******************************************************************************************************<br /></p>
<pre>
#!/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";
</pre>
]]>
</platform_settings>
</flagsdescription>
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