[cgl_discussion] [Fwd: [ANNOUNCE] Native POSIX Thread Library 0.1]

Brian Stevens bstevens at redhat.com
Fri Sep 20 14:46:33 PDT 2002


It is reasonable to expect it will be backported to 2.4.x soon.

Brian

Craig Thomas wrote:

>It says here that the build environment (to build the threaded
>library) must be 2.5, so I am assuming that it is implied that the
>library will be released on 2.5.  This looks like something to consider,
>but will there be a need to have this back ported to 2.4.18?
>
>On Fri, 2002-09-20 at 09:25, Khalid Aziz wrote:
>
>>Here is another implementation of POSIX threads. Might be interesting
>>for POSIX threads project to look at. People have already started asking
>>for comparison with NGPT on lkml.
>>
>>--
>>Khalid
>>
>>Ulrich Drepper wrote:
>>
>>>-----BEGIN PGP SIGNED MESSAGE-----
>>>Hash: SHA1
>>>
>>>We are pleased to announce the first publically available source
>>>release of a new POSIX thread library for Linux.  As part of the
>>>continuous effort to improve Linux's capabilities as a client, server,
>>>and computing platform Red Hat sponsored the development of this
>>>completely new implementation of a POSIX thread library, called Native
>>>POSIX Thread Library, NPTL.
>>>
>>>Unless major flaws in the design are found this code is intended to
>>>become the standard POSIX thread library on Linux system and it will
>>>be included in the GNU C library distribution.
>>>
>>>The work visible here is the result of close collaboration of kernel
>>>and runtime developers.  The collaboration proceeded by developing the
>>>kernel changes while writing the appropriate parts of the thread
>>>library.  Whenever something couldn't be implemented optimally some
>>>interface was changed to eliminate the issue.  The result is this
>>>thread library which is, unlike previous attempts, a very thin layer
>>>on top of the kernel.  This helps to achieve a maximum of performance
>>>for a minimal price.
>>>
>>>A white paper (still in its draft stage, though) describing the design
>>>is available at
>>>
>>>   http://people.redhat.com/drepper/nptl-design.pdf
>>>
>>>It provides a larger number of details on the design and insight into
>>>the design process.  At this point we want to repeat only a few
>>>important points:
>>>
>>>- - the new library is based on an 1-on-1 model.  Earlier design
>>>   documents stated that an M-on-N implementation was necessary to
>>>   support a scalable thread library.  This was especially true for
>>>   the IA-32 and x86-64 platforms since the ABI with respect to threads
>>>   forces the use of segment registers and the only way to use those
>>>   registers was with the Local Descriptor Table (LDT) data structure
>>>   of the processor.
>>>
>>>   The kernel limitations the earlier designs were based on have been
>>>   eliminated as part of this project, opening the road to a 1-on-1
>>>   implementation which has many advantages such as
>>>
>>>   + less complex implementation;
>>>   + avoidance of two-level scheduling, enabling the kernel to make all
>>>     scheduling decisions;
>>>   + direct interaction between kernel and user-level code (e.g., when
>>>     delivering signals);
>>>   + and more and more.
>>>
>>>   It is not generally accepted that a 1-on-1 model is superior but our
>>>   tests showed the viability of this approach and by comparing it with
>>>   the overhead added by existing M-on-N implementations we became
>>>   convinced that 1-on-1 is the right approach.
>>>
>>>   Initial confirmations were test runs with huge numbers of threads.
>>>   Even on IA-32 with its limited address space and memory handling
>>>   running 100,000 concurrent threads was no problem at all, creating
>>>   and destroying the threads did not take more than two seconds.  This
>>>   all was made possible by the kernel work performed as part of this
>>>   project.
>>>
>>>   The only limiting factors on the number of threads today are
>>>   resource availability (RAM and processor resources) and architecture
>>>   limitations.  Since every thread needs at least a stack and data
>>>   structures describing the thread the number is capped.  On 64-bit
>>>   machines the architecture does not add any limitations anymore (at
>>>   least for the moment) and with enough resources the number of
>>>   threads can be grown arbitrarily.
>>>
>>>   This does not mean that using hundreds of thousands of threads is a
>>>   desirable design for the majority of applications.  At least not
>>>   unless the number of processors matches the number of threads.  But
>>>   it is important to note that the design on the library does not have
>>>   a fixed limit.
>>>
>>>   The kernel work to optimize for a high thread count is still
>>>   ongoing.  Some places in which the kernel iterates over process and
>>>   threads remain and other places need to be cleaned up.  But it has
>>>   already been shown that given sufficient resources and a reasonable
>>>   architecture an order of magnitude more threads can be created than
>>>   in our tests on IA-32.
>>>
>>>- - The futex system call is used extensively in all synchronization
>>>   primitives and other places which need some kind of
>>>   synchronization.  The futex mechanism is generic enough to support
>>>   the standard POSIX synchronization mechanisms with very little
>>>   effort.
>>>
>>>   The fact that this is possible is also essential for the selection
>>>   of the 1-on-1 model since only with the kernel seeing all the
>>>   waiters and knowing that they are blocked for synchronization
>>>   purposes will allow the scheduler to make decisions as good as a
>>>   thread library would be able to in an M-on-N model implementation.
>>>
>>>   Futexes also allow the implementation of inter-process
>>>   synchronization primitives, a sorely missed feature in the old
>>>   LinuxThreads implementation (Hi jbj!).
>>>
>>>- - Substantial effort went into making the thread creation and
>>>   destruction as fast as possible.  Extensions to the clone(2) system
>>>   call were introduced to eliminate the need for a helper thread in
>>>   either creation or destruction.  The exit process in the kernel was
>>>   optimized (previously not a high priority).  The library itself
>>>   optimizes the memory allocation so that in many cases the creation
>>>   of a new thread can be achieved with one single system call.
>>>
>>>   On an old IA-32 dual 450MHz PII Xeon system 100,000 threads can be
>>>   created and destroyed in 2.3 secs (with up to 50 threads running at
>>>   any one time).
>>>
>>>- - Programs indirectly linked against the thread library had problems
>>>   with the old implementation because of the way symbols are looked
>>>   up. This should not be a problem anymore.
>>>
>>>The thread library is designed to be binary compatible with the old
>>>LinuxThreads implementation.  This compatibility obviously has some
>>>limitations.  In places where the LinuxThreads implementation diverged
>>>from the POSIX standard incompatibilities exist.  Users of the old
>>>library have been warned from day one that this day will come and code
>>>which added work-arounds for the POSIX non-compliance better be
>>>prepared to remove that code.  The visible changes of the library
>>>include:
>>>
>>>- - The signal handling changes from per-thread signal handling to the
>>>   POSIX process signal handling.  This change will require changes in
>>>   programs which exploit the non-conformance of the old implementation.
>>>
>>>   One consequence of this is that SIGSTOP works on the process.  Job
>>>control
>>>   in the shell and stopping the whole process in a debugger work now.
>>>
>>>- - getpid() now returns the same value in all threads
>>>
>>>- - the exec functions are implemented correctly: the exec'ed process gets
>>>   the PID of the process.  The parent of the multi-threaded application
>>>   is only notified when the exec'ed process terminates.
>>>
>>>- - thread handlers registered with pthread_atfork are not anymore run
>>>   if vfork is used.  This isn't required by the standard (which does
>>>   not define vfork) and all which is allowed in the child is calling
>>>   exit() or an exec function.  A user of vfork better knows what s/he
>>>   does.
>>>
>>>- - libpthread should now be much more resistant to linking problems: even
>>>   if the application doesn't list libpthread as a direct dependency
>>>   functions which are extended by libpthread should work correctly.
>>>
>>>- - no manager thread
>>>
>>>- - inter-process mutex, read-write lock, conditional variable, and barrier
>>>   implementations are available
>>>
>>>- - the pthread_kill_other_threads_np function is not available.  It was
>>>   needed to work around the broken signal handling.  If somebody shows
>>>   some existing code which makes legitimate use of this function we
>>>   might add it back.
>>>
>>>- - requires a kernel with the threading capabilities of Linux 2.5.36.
>>>
>>>The sources for the new library are for the time being available at
>>>
>>>   ftp://people.redhat.com/drepper/nptl/
>>>
>>>The current sources contain support only for IA-32 but this will
>>>change very quickly.  The thread library is built as part of glibc so
>>>the complete set of glibc sources is available as well.  The current
>>>snapshot for glibc 2.3 (or glibc 2.3 when released) is necessary.  You
>>>can find it at
>>>
>>>   ftp://sources.redhat.com/pub/glibc/snapshots
>>>
>>>Final releases will be available on ftp.gnu.org and its mirrors.
>>>
>>>Building glibc with the new thread library is demanding on the
>>>compilation environment.
>>>
>>>- - The 2.5.36 kernel or above must be installed and used.  To compile
>>>   glibc it is necessary to create the symbolic link
>>>
>>>      /lib/modules/$(uname -r)/build
>>>
>>>   to point to the build directory.
>>>
>>>- - The general compiler requirement for glibc is at least gcc 3.2.  For
>>>   the new thread code it is even necessary to have working support for
>>>   the __thread keyword.
>>>
>>>   Similarly, binutils with functioning TLS support are needed.
>>>
>>>   The (Null) beta release of the upcoming Red Hat Linux product is
>>>   known to have the necessary tools available after updating from the
>>>   latest binaries on the FTP site.  This is no ploy to force everybody
>>>   to use Red Hat Linux, it's just the only environment known to date
>>>   which works.  If alternatives are known they can be announced on the
>>>   mailing list.
>>>
>>>- - To configure glibc it is necessary to run in the build directory
>>>   (which always should be separate from the source directory):
>>>
>>>    /path/to/glibc/configure --prefix=/usr --enable-add-ons=linuxthreads2 \
>>>       --enable-kernel=current --with-tls
>>>
>>>   The --enable-kernel parameter requires that the 2.5.36+ kernel is
>>>   running.  It is not strictly necessary but helps to avoid mistakes.
>>>   It might also be a good idea to add --disable-profile, just to speed
>>>   up the compilation.
>>>
>>>   When configured as above the library must not be installed since it
>>>   would overwrite the system's library.  If you want to install the
>>>   resulting library choose a different --prefix parameter value.
>>>   Otherwise the new code can be used without installation.  Running
>>>   existing binaries is possible with
>>>
>>>    elf/ld.so --library-path .:linuxthreads2:dlfcn:math <binary> <args>...
>>>
>>>   Alternatively the binary could be build to find the dynamic linker
>>>   and DSO by itself.  This is a much easier way to debug the code
>>>   since gdb can start the binary.  Compiling is a bit more complicated
>>>   in this case:
>>>
>>>    gcc -nostdlib -nostartfiles -o <OUTPUT> csu/crt1.o csu/crti.o \
>>>      $(gcc --print-file-name=crtbegin.o) <INPUTS> \
>>>      -Wl,-rpath,$PWD,-dynamic-linker,$PWD/ld-linux.so.2 \
>>>      linuxthreads2/libpthread.so.0 ./libc.so.6 ./libc_nonshared.a \
>>>      elf/ld-linux.so.2 $(gcc --print-file-name=crtend.o) csu/crtn.o
>>>
>>>   This command assumes that it is run in the build directory.  Correct
>>>   the paths if necessary.  The compilation will use the system's
>>>   headers which is a good test but might lead to strange effects if
>>>   there are compatibility bugs left.
>>>
>>>Once all these prerequisites are met compiling glibc should be easy.
>>>But there are some tests which will flunk.  For good reasons we aren't
>>>officially releasing the code yet.  The bugs are either in the TLS
>>>code which is not enabled in the standard glibc build, or obviously in
>>>the thread library itself.  To run the tests for the thread library
>>>run
>>>
>>>   make subdirs=linuxthreads2 check
>>>
>>>One word on the name 'linuxthreads2' of the directory.  This is only a
>>>convenience thing so that the glibc configure scripts don't complain
>>>about missing thread support.  It will we changed to reflect the real
>>>name of the library ASAP.
>>>
>>>What can you expect?
>>>
>>>This is a very early version of the code so the obvious answer is:
>>>some problems.  The test suite for the new thread code should pass but
>>>beside that and some performance measurement tool we haven't run much
>>>code.  Ideally we would get people to write many more of these small
>>>test programs which are included in the sources.  Compiling big
>>>programs would mean not being able to locate problems easy.  But I
>>>certainly won't object to people running and debugging bigger
>>>applications.  Please report successes and failures to the mailing
>>>list.
>>>
>>>People who are interested in contributing must be aware that for any
>>>non-trivial change we need an assignment of the code to the FSF.  The
>>>process is unfortunately necessary in today's world.
>>>
>>>People who are contaminated by having worked on proprietary thread
>>>library implementation should not participate in discussions on the
>>>mailing list unless they willfully disclose the information.  Every
>>>bit of information is publically available from the mailing list
>>>archive.
>>>
>>>Which brings us to the final point: the mailing list for *all*
>>>discussions related to this thread library implementation is
>>>
>>>   phil-list at redhat.com
>>>
>>>Go to
>>>
>>>   https://listman.redhat.com/mailman/listinfo/phil-list
>>>
>>>to subscribe, unsubscribe, or review the archive.
>>>
>>>- --
>>>- ---------------.                          ,-.   1325 Chesapeake Terrace
>>>Ulrich Drepper  \    ,-------------------'   \  Sunnyvale, CA 94089 USA
>>>Red Hat          `--' drepper at redhat.com   `------------------------
>>>-----BEGIN PGP SIGNATURE-----
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>>>
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>>>fA5OFtNuzYqltxSMoL8Ambw=
>>>=4pb4
>>>-----END PGP SIGNATURE-----
>>>
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>>>
>>====================================================================
>>Khalid Aziz                                   Linux Systems Division
>>(970)898-9214                                        Hewlett-Packard
>>khalid at fc.hp.com                                    Fort Collins, CO
>>
>>"The Linux kernel is subject to relentless development" 
>>				- Alessandro Rubini
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>>





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