make.settings.localfile. Note: this will produce some warnings and abort with an error, which is intended.
make.settings.localfile according to your system configuration:
STXXLroot directory (
STXXLto use Boost libraries (you should have the Boost libraries already installed)
BOOST_ROOTvariable to the Boost root path, unless Boost is installed in system default search paths.
STXXLto use the libstdc++ parallel mode
tests_g++_pmodeinstead of the ones listed below
STXXLto use the MCSTL library (you should have the MCSTL library already installed)
MCSTL_ROOTvariable to the MCSTL root path
tests_g++_mcstlinstead of the ones listed below
-O3or other g++ optimization level you like (default:
-gor other g++ debugging option if you want to produce a debug version of the Stxxl library or Stxxl examples (default: not set)
make.settings.gnu, they are usually overridden by settings in
LDFLAGS, for example, you can add arbitrary compiler and linker options
After compiling the library, some Makefile variables are written to
pmstxxl.mk if you have built with parallel mode,
mcstxxl.mk if you have built with MCSTL) in your
STXXL_ROOT directory. This file should be included from your application's Makefile.
The following variables can be used:
STXXL_CXX- the compiler used to build the
STXXLlibrary, it's recommended to use the same to build your applications
STXXL_CPPFLAGS- add these flags to the compile commands
STXXL_LDLIBS- add these libraries to the link commands
An example Makefile for an application using
STXXL_ROOT ?= .../stxxl STXXL_CONFIG ?= stxxl.mk include $(STXXL_ROOT)/$(STXXL_CONFIG) # use the variables from stxxl.mk CXX = $(STXXL_CXX) CPPFLAGS += $(STXXL_CPPFLAGS) LDLIBS += $(STXXL_LDLIBS) # add your own optimization, warning, debug, ... flags # (these are *not* set in stxxl.mk) CPPFLAGS += -O3 -Wall -g -DFOO=BAR # build your application # (my_example.o is generated from my_example.cpp automatically) my_example.bin: my_example.o $(CXX) $(CXXFLAGS) $(CPPFLAGS) $(LDFLAGS) my_example.o -o $@ $(LDLIBS)
To enable (shared-memory-)parallel execution of internal computation (in fact, sorting and merging, and random shuffling), you have several options depending on the compiler version used:
STXXL_PARALLEL_MODE_EXPLICITand enabling OpenMP (
-fopenmp) during compilation and linkage of your program. Compiling the library binary with this flag enabled is not really necessary, since the most time-consuming operations are called by the generic routines and thus contained in the header files.
_GLIBCXX_PARALLELand enabling OpenMP (
-fopenmp). This has the implication that STL algorithms in your program will also be executed in parallel, which may have undesired side effects. These options are automatically used when you built STXXL using the
*_pmodetarget, and your Makefile includes
*_mcstltarget, and your Makefile includes
We recommend to try the first option at first.
The number of threads to be used can be set by the environment variable OMP_NUM_THREADS or by calling omp_set_num_threads. Detailed tuning can be achieved as described here.
Before you try to run one of the
STXXL examples (or your own
STXXL program) you must configure the disk space that will be used as external memory for the library.
To get best performance with
STXXL you should assign separate disks to it. These disks should be used by the library only. Since
STXXL is developed to exploit disk parallelism, the performance of your external memory application will increase if you use more than one disk. But from how many disks your application can benefit depends on how "I/O bound" it is. With modern disk bandwidths of about 50-75 MiB/s most of applications are I/O bound for one disk. This means that if you add another disk the running time will be halved. Adding more disks might also increase performance significantly.
The library benefits from direct transfers from user memory to disk, which saves superfluous copies. We recommend to use the
XFS file system, which gives good read and write performance for large files. Note that file creation speed of
XFS is a bit slower, so that disk files should be precreated for optimal performance.
If the filesystems only use is to store one large
STXXL disk file, we also recommend to add the following options to the
mkfs.xfs command to gain maximum performance:
-d agcount=1 -l size=512b
The following filesystems have been reported not to support direct I/O:
glusterfs . Since direct I/O is enabled by default, you may recompile
STXXL_DIRECT_IO_OFF defined to access files on these file systems.
You must define the disk configuration for an
STXXL program in a file named
'.stxxl' that must reside in the same directory where you execute the program. You can change the default file name for the configuration file by setting the environment variable
Each line of the configuration file describes a disk. A disk description uses the following format:
Description of the parameters:
full_disk_filename: full disk filename. In order to access disks STXXL uses file access methods. Each disk is represented as a file. If you have a disk that is mounted in Unix to the path /mnt/disk0/, then the correct value for the
capacity: maximum capacity of the disk in megabytes (0 means autogrow, file will be deleted afterwards)
STXXLhas a number of different file access implementations for POSIX systems, choose one of them:
writesystem calls which perform disk transfers directly on user memory pages without superfluous copying (currently the fastest method)
boostfd: access the file using a Boost file descriptor
fileperblock_boostfd: same as above, but take a single file per block, using full_disk_filename as file name prefix. Usually provide worse performance than the standard variants, but release freed blocks to the file system immediately.
simdisk: simulates timings of the IBM IC35L080AVVA07 disk, full_disk_filename must point to a file on a RAM disk partition with sufficient space
memory: keeps all data in RAM, for quicker testing
wbtl: library-based write-combining (good for writing small blocks onto SSDs), based on
See also the example configuration file
'config_example' included in the tarball.
STXXL produces two kinds of log files, a message and an error log. By setting the environment variables
STXXLERRLOGFILE, you can configure the location of these files. The default values are
In order to get the maximum performance one should precreate disk files described in the configuration file, before running
The precreation utility is included in the set of
STXXL utilities (
utils/createdisks.bin ). Run this utility for each disk you have defined in the disk configuration file:
utils/createdisks.bin capacity full_disk_filename...